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Voltage Tolerant xproms

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  • Bill Rowe
    working with the MSI/88e I find that its VCC can be anywhere from 4.5V to over 6V depending on the state of the batteries. It works fine with its own ROM but
    Message 1 of 11 , Sep 16, 2008
    • 0 Attachment
      working with the MSI/88e I find that its VCC can be anywhere from 4.5V to over 6V depending on the state of the batteries. It works fine with its own ROM but I'm getting way flaky results with my eeproms which want 4.5-5V and seem quite sticky about it(at least I'm hoping this is what's behind the flakiness).

      I looked at 2764s and they also say 5V plus or minus 10%. Anybody know of a more tolerant alternative? It's easier for me to be sure of >5V than less.


      ----- Original Message -----
      From: Bill Rowe
      To: cosmacelf@yahoogroups.com
      Sent: Monday, June 23, 2008 8:09 AM
      Subject: [cosmacelf] MSI88/e Running the IDIOT/4 Monitor


      As of this morning I have the idiot/4 monitor running in the MSI/88e - can
      you say woohoo!

      I need to get a better serial connection going now so i can start exploring
      the hardware. The picture below shows my moment of victory with the
      semi-eviscerated MSI box connected to my laptop via the arduino breadboard.
      If you have very tiny eyes you can make out the idiot/4 prompt on the laptop
      screen amid all the debug clutter.

      Again, woohoo! Thanks again to dave for sending me the 88e and to lee and
      others for their work on the cpu schematic.

      http://groups.yahoo.com/group/cosmacelf/files/MSI88CPU/MSI_IDIOT.jpg
      ----- Original Message -----
      From: Bill Rowe
      To: cosmacelf@yahoogroups.com
      Sent: Sunday, June 22, 2008 7:37 PM
      Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

      thanks lee. The version of idiot/4 that i'm working with is 1K with the
      register saving routines built in and it finds its own ram.

      I don't have it working in the MSI/88e yet but i'm getting there. I'm at a
      point now where I know it's running and waiting for a serial input - won't
      be long now.
      ----- Original Message -----
      From: Lee Hart
      To: cosmacelf@yahoogroups.com
      Sent: Sunday, June 22, 2008 3:08 PM
      Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

      randy129 wrote:
      >>> I assembled the TMSI BASIC source, configured for 8K ROM
      >>> (PAGE=2000H)

      bill rowe wrote:
      >> This is too funny, I'm in a time warp loop back to where Dave was
      >> five years ago - hope I have better luck! I can see one thing that
      >> might have been wrong if the idiot monitor assumed RAM at 2000.
      >> There may be ram there but it might well cause an address conflict
      >> with an eeprom.

      > I thought you said the RAM in yours was at 8000?
      > I don't see the unassembled source for either the plain
      > IDIOT, or the combo with tiny basic. Seems like it would
      > be a lot of work to convert the listing back to plain source.
      > dfnr2 says he assembled it, maybe he still has the source?

      It's been a long time; but if I remember correctly the IDIOT monitor
      itself doesn't need any RAM at all, and can be located anywhere in
      memory that you have 512 bytes available.

      When you add BASIC and the register save/restore features, then it needs
      RAM; and it will therefore need to be assembled accordingly (and have
      RAM at the intended locations). I think I set it up so a 4K ROM could
      have the IDIOT monitor and BASIC, and would occupy addresses 0-1FFF. The
      RAM would then start at 2000h (just above this ROM) and could go as high
      as you liked.

      --
      Ring the bells that still can ring
      Forget the perfect offering
      There is a crack in everything
      That's how the light gets in -- Leonard Cohen
      --
      Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

      ----------------------------------------------------------

      No virus found in this incoming message.
      Checked by AVG.
      Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008
      11:52 AM

      [Non-text portions of this message have been removed]

      No virus found in this incoming message.
      Checked by AVG.
      Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008
      11:52 AM






      ------------------------------------------------------------------------------


      No virus found in this incoming message.
      Checked by AVG.
      Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008 11:52 AM


      [Non-text portions of this message have been removed]
    • rdoerr@bizserve.com
      Have you thought about adding a 5.1v Zener across the power supply to help limit the voltage to about 5.1V? I ve seen that trick used to help limit the over
      Message 2 of 11 , Sep 16, 2008
      • 0 Attachment
        Have you thought about adding a 5.1v Zener across the
        power supply to help limit the voltage to about 5.1V?
        I've seen that trick used to help limit the over
        voltage on battery operated systems.

        Some google searches about zener diode voltage
        regulation may turn up some example schematics.

        In regards to the "flakyness" have you been able to
        determine if it acts fine at a solid 5V but not at a
        higher voltage like 6V? Can you hook up the system
        to a nice regulated 5V bench supply to verify it
        works ok there? At least that way you can point to
        power being a possible problem.

        Just a couple things to check.

        Robert

        ------- Original Message -------
        From : Bill Rowe[mailto:bill_rowe@...]
        Sent : 9/16/2008 7:50:56 PM
        To : cosmacelf@yahoogroups.com
        Cc :
        Subject : RE: [cosmacelf] Voltage Tolerant xproms

        working with the MSI/88e I find that its VCC can be
        anywhere from 4.5V to over 6V depending on the state
        of the batteries. It works fine with its own ROM but
        I'm getting way flaky results with my eeproms which
        want 4.5-5V and seem quite sticky about it(at least
        I'm hoping this is what's behind the flakiness).

        I looked at 2764s and they also say 5V plus or minus
        10%. Anybody know of a more tolerant alternative?
        It's easier for me to be sure of >5V than less.


        ----- Original Message -----
        From: Bill Rowe
        To: cosmacelf@yahoogroups.com
        Sent: Monday, June 23, 2008 8:09 AM
        Subject: [cosmacelf] MSI88/e Running the IDIOT/4
        Monitor


        As of this morning I have the idiot/4 monitor
        running in the MSI/88e - can
        you say woohoo!

        I need to get a better serial connection going now
        so i can start exploring
        the hardware. The picture below shows my moment of
        victory with the
        semi-eviscerated MSI box connected to my laptop via
        the arduino breadboard.
        If you have very tiny eyes you can make out the
        idiot/4 prompt on the laptop
        screen amid all the debug clutter.

        Again, woohoo! Thanks again to dave for sending me
        the 88e and to lee and
        others for their work on the cpu schematic.


        http://groups.yahoo.com/group/cosmacelf/files/MSI88CPU/MSI_IDIOT.jpg

        ----- Original Message -----
        From: Bill Rowe
        To: cosmacelf@yahoogroups.com
        Sent: Sunday, June 22, 2008 7:37 PM
        Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

        thanks lee. The version of idiot/4 that i'm working
        with is 1K with the
        register saving routines built in and it finds its
        own ram.

        I don't have it working in the MSI/88e yet but i'm
        getting there. I'm at a
        point now where I know it's running and waiting for
        a serial input - won't
        be long now.
        ----- Original Message -----
        From: Lee Hart
        To: cosmacelf@yahoogroups.com
        Sent: Sunday, June 22, 2008 3:08 PM
        Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

        randy129 wrote:
        >>> I assembled the TMSI BASIC source, configured
        for 8K ROM
        >>> (PAGE=2000H)

        bill rowe wrote:
        >> This is too funny, I'm in a time warp loop back
        to where Dave was
        >> five years ago - hope I have better luck! I can
        see one thing that
        >> might have been wrong if the idiot monitor
        assumed RAM at 2000.
        >> There may be ram there but it might well cause
        an address conflict
        >> with an eeprom.

        > I thought you said the RAM in yours was at 8000?
        > I don't see the unassembled source for either the
        plain
        > IDIOT, or the combo with tiny basic. Seems like
        it would
        > be a lot of work to convert the listing back to
        plain source.
        > dfnr2 says he assembled it, maybe he still has
        the source?

        It's been a long time; but if I remember correctly
        the IDIOT monitor
        itself doesn't need any RAM at all, and can be
        located anywhere in
        memory that you have 512 bytes available.

        When you add BASIC and the register save/restore
        features, then it needs
        RAM; and it will therefore need to be assembled
        accordingly (and have
        RAM at the intended locations). I think I set it up
        so a 4K ROM could
        have the IDIOT monitor and BASIC, and would occupy
        addresses 0-1FFF. The
        RAM would then start at 2000h (just above this ROM)
        and could go as high
        as you liked.

        --
        Ring the bells that still can ring
        Forget the perfect offering
        There is a crack in everything
        That's how the light gets in -- Leonard Cohen
        --
        Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
        leeahart_at_earthlink.net


        ----------------------------------------------------------

        No virus found in this incoming message.
        Checked by AVG.
        Version: 7.5.524 / Virus Database: 270.4.1/1511 -
        Release Date: 20/06/2008
        11:52 AM

        [Non-text portions of this message have been removed]

        No virus found in this incoming message.
        Checked by AVG.
        Version: 7.5.524 / Virus Database: 270.4.1/1511 -
        Release Date: 20/06/2008
        11:52 AM






        ------------------------------------------------------------------------------


        No virus found in this incoming message.
        Checked by AVG.
        Version: 7.5.524 / Virus Database: 270.4.1/1511 -
        Release Date: 20/06/2008 11:52 AM


        [Non-text portions of this message have been removed]


        ------------------------------------

        ========================================================
        Visit the COSMAC ELF website at
        http://www.cosmacelf.comYahoo! Groups Links
      • Raymond Siminas
        Connecting a zener diode directly across the power supply is NOT a good idea.  If the power supply reaches the zener diode voltage. when the zener breaks down
        Message 3 of 11 , Sep 16, 2008
        • 0 Attachment
          Connecting a zener diode directly across the power supply is NOT a good idea.  If the power supply reaches the zener diode voltage. when the zener breaks down (it's normal reaction), the power supply may see a very low resistance and go into overcurrent mode.  If it does, there's a good chance that the zener diode many be destroyed in the process.  Zener diodes should have a series resistor chosen to  drop the voltage applied to it minue the zener diode voltage and be rated to daw about 1/10 the current (if memory serves) that the zener draws at full rating.  This is to bias the zener diode to provide it's rated voltage under no load conditions.  The power rating of the series resistor should be chosen such that the maximum current that will flow through it times the voltage being dropped across it,  equals the power rating.  It's a good idea to go up to the next wattage rating just for the sake of a little geadroom..


           




          --- On Tue, 9/16/08, rdoerr@... <rdoerr@...> wrote:

          From: rdoerr@... <rdoerr@...>
          Subject: RE: [cosmacelf] Voltage Tolerant xproms
          To: cosmacelf@yahoogroups.com
          Date: Tuesday, September 16, 2008, 5:47 PM






          Have you thought about adding a 5.1v Zener across the
          power supply to help limit the voltage to about 5.1V?
          I've seen that trick used to help limit the over
          voltage on battery operated systems.

          Some google searches about zener diode voltage
          regulation may turn up some example schematics.

          In regards to the "flakyness" have you been able to
          determine if it acts fine at a solid 5V but not at a
          higher voltage like 6V? Can you hook up the system
          to a nice regulated 5V bench supply to verify it
          works ok there? At least that way you can point to
          power being a possible problem.

          Just a couple things to check.

          Robert

          ------- Original Message -------
          From : Bill Rowe[mailto:bill_rowe@rogers. com]
          Sent : 9/16/2008 7:50:56 PM
          To : cosmacelf@yahoogrou ps.com
          Cc :
          Subject : RE: [cosmacelf] Voltage Tolerant xproms

          working with the MSI/88e I find that its VCC can be
          anywhere from 4.5V to over 6V depending on the state
          of the batteries. It works fine with its own ROM but
          I'm getting way flaky results with my eeproms which
          want 4.5-5V and seem quite sticky about it(at least
          I'm hoping this is what's behind the flakiness).

          I looked at 2764s and they also say 5V plus or minus
          10%. Anybody know of a more tolerant alternative?
          It's easier for me to be sure of >5V than less.

          ----- Original Message -----
          From: Bill Rowe
          To: cosmacelf@yahoogrou ps.com
          Sent: Monday, June 23, 2008 8:09 AM
          Subject: [cosmacelf] MSI88/e Running the IDIOT/4
          Monitor

          As of this morning I have the idiot/4 monitor
          running in the MSI/88e - can
          you say woohoo!

          I need to get a better serial connection going now
          so i can start exploring
          the hardware. The picture below shows my moment of
          victory with the
          semi-eviscerated MSI box connected to my laptop via
          the arduino breadboard.
          If you have very tiny eyes you can make out the
          idiot/4 prompt on the laptop
          screen amid all the debug clutter.

          Again, woohoo! Thanks again to dave for sending me
          the 88e and to lee and
          others for their work on the cpu schematic.

          http://groups. yahoo.com/ group/cosmacelf/ files/MSI88CPU/ MSI_IDIOT. jpg

          ----- Original Message -----
          From: Bill Rowe
          To: cosmacelf@yahoogrou ps.com
          Sent: Sunday, June 22, 2008 7:37 PM
          Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

          thanks lee. The version of idiot/4 that i'm working
          with is 1K with the
          register saving routines built in and it finds its
          own ram.

          I don't have it working in the MSI/88e yet but i'm
          getting there. I'm at a
          point now where I know it's running and waiting for
          a serial input - won't
          be long now.
          ----- Original Message -----
          From: Lee Hart
          To: cosmacelf@yahoogrou ps.com
          Sent: Sunday, June 22, 2008 3:08 PM
          Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

          randy129 wrote:
          >>> I assembled the TMSI BASIC source, configured
          for 8K ROM
          >>> (PAGE=2000H)

          bill rowe wrote:
          >> This is too funny, I'm in a time warp loop back
          to where Dave was
          >> five years ago - hope I have better luck! I can
          see one thing that
          >> might have been wrong if the idiot monitor
          assumed RAM at 2000.
          >> There may be ram there but it might well cause
          an address conflict
          >> with an eeprom.

          > I thought you said the RAM in yours was at 8000?
          > I don't see the unassembled source for either the
          plain
          > IDIOT, or the combo with tiny basic. Seems like
          it would
          > be a lot of work to convert the listing back to
          plain source.
          > dfnr2 says he assembled it, maybe he still has
          the source?

          It's been a long time; but if I remember correctly
          the IDIOT monitor
          itself doesn't need any RAM at all, and can be
          located anywhere in
          memory that you have 512 bytes available.

          When you add BASIC and the register save/restore
          features, then it needs
          RAM; and it will therefore need to be assembled
          accordingly (and have
          RAM at the intended locations). I think I set it up
          so a 4K ROM could
          have the IDIOT monitor and BASIC, and would occupy
          addresses 0-1FFF. The
          RAM would then start at 2000h (just above this ROM)
          and could go as high
          as you liked.

          --
          Ring the bells that still can ring
          Forget the perfect offering
          There is a crack in everything
          That's how the light gets in -- Leonard Cohen
          --
          Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
          leeahart_at_ earthlink. net

          ------------ --------- --------- --------- --------- --------- -

          No virus found in this incoming message.
          Checked by AVG.
          Version: 7.5.524 / Virus Database: 270.4.1/1511 -
          Release Date: 20/06/2008
          11:52 AM

          [Non-text portions of this message have been removed]

          No virus found in this incoming message.
          Checked by AVG.
          Version: 7.5.524 / Virus Database: 270.4.1/1511 -
          Release Date: 20/06/2008
          11:52 AM

          ------------ --------- --------- --------- --------- --------- -

          No virus found in this incoming message.
          Checked by AVG.
          Version: 7.5.524 / Virus Database: 270.4.1/1511 -
          Release Date: 20/06/2008 11:52 AM

          [Non-text portions of this message have been removed]

          ------------ --------- --------- ------

          ============ ========= ========= ========= ========= ========
          Visit the COSMAC ELF website at
          http://www.cosmacel f.comYahoo! Groups Links















          [Non-text portions of this message have been removed]
        • Raymond Siminas
          The EEPROMS havea tighter voltage tolerance than typical CMOS parts mainly because they re normally used with the TTL logic families which want +5V +/-
          Message 4 of 11 , Sep 16, 2008
          • 0 Attachment
            The EEPROMS havea tighter voltage tolerance than typical CMOS parts mainly because they're normally used with the TTL logic families which want +5V +/- 0.25VDC.  I've seen TTL devices get the snot blown out of them by running at 6V, and I've seen some work fine after seeing that much.  It's hit or miss.  Myself, I wouldn't run anything using TTL parts on batteries without using more battery voltage than necessary, and feeding the battery voltage into at least a low dropout voltage regulator.  Batteries are just not that stable in my opinion.  I'm not sure how easy it will be to find more voltage tolerant EEPROMS in the commercial market.


             




            --- On Tue, 9/16/08, Bill Rowe <bill_rowe@...> wrote:

            From: Bill Rowe <bill_rowe@...>
            Subject: [cosmacelf] Voltage Tolerant xproms
            To: cosmacelf@yahoogroups.com
            Date: Tuesday, September 16, 2008, 4:50 PM






            working with the MSI/88e I find that its VCC can be anywhere from 4.5V to over 6V depending on the state of the batteries. It works fine with its own ROM but I'm getting way flaky results with my eeproms which want 4.5-5V and seem quite sticky about it(at least I'm hoping this is what's behind the flakiness).

            I looked at 2764s and they also say 5V plus or minus 10%. Anybody know of a more tolerant alternative? It's easier for me to be sure of >5V than less.

            ----- Original Message -----
            From: Bill Rowe
            To: cosmacelf@yahoogrou ps.com
            Sent: Monday, June 23, 2008 8:09 AM
            Subject: [cosmacelf] MSI88/e Running the IDIOT/4 Monitor

            As of this morning I have the idiot/4 monitor running in the MSI/88e - can
            you say woohoo!

            I need to get a better serial connection going now so i can start exploring
            the hardware. The picture below shows my moment of victory with the
            semi-eviscerated MSI box connected to my laptop via the arduino breadboard.
            If you have very tiny eyes you can make out the idiot/4 prompt on the laptop
            screen amid all the debug clutter.

            Again, woohoo! Thanks again to dave for sending me the 88e and to lee and
            others for their work on the cpu schematic.

            http://groups. yahoo.com/ group/cosmacelf/ files/MSI88CPU/ MSI_IDIOT. jpg
            ----- Original Message -----
            From: Bill Rowe
            To: cosmacelf@yahoogrou ps.com
            Sent: Sunday, June 22, 2008 7:37 PM
            Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

            thanks lee. The version of idiot/4 that i'm working with is 1K with the
            register saving routines built in and it finds its own ram.

            I don't have it working in the MSI/88e yet but i'm getting there. I'm at a
            point now where I know it's running and waiting for a serial input - won't
            be long now.
            ----- Original Message -----
            From: Lee Hart
            To: cosmacelf@yahoogrou ps.com
            Sent: Sunday, June 22, 2008 3:08 PM
            Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

            randy129 wrote:
            >>> I assembled the TMSI BASIC source, configured for 8K ROM
            >>> (PAGE=2000H)

            bill rowe wrote:
            >> This is too funny, I'm in a time warp loop back to where Dave was
            >> five years ago - hope I have better luck! I can see one thing that
            >> might have been wrong if the idiot monitor assumed RAM at 2000.
            >> There may be ram there but it might well cause an address conflict
            >> with an eeprom.

            > I thought you said the RAM in yours was at 8000?
            > I don't see the unassembled source for either the plain
            > IDIOT, or the combo with tiny basic. Seems like it would
            > be a lot of work to convert the listing back to plain source.
            > dfnr2 says he assembled it, maybe he still has the source?

            It's been a long time; but if I remember correctly the IDIOT monitor
            itself doesn't need any RAM at all, and can be located anywhere in
            memory that you have 512 bytes available.

            When you add BASIC and the register save/restore features, then it needs
            RAM; and it will therefore need to be assembled accordingly (and have
            RAM at the intended locations). I think I set it up so a 4K ROM could
            have the IDIOT monitor and BASIC, and would occupy addresses 0-1FFF. The
            RAM would then start at 2000h (just above this ROM) and could go as high
            as you liked.

            --
            Ring the bells that still can ring
            Forget the perfect offering
            There is a crack in everything
            That's how the light gets in -- Leonard Cohen
            --
            Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_ earthlink. net

            ------------ --------- --------- --------- --------- --------- -

            No virus found in this incoming message.
            Checked by AVG.
            Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008
            11:52 AM

            [Non-text portions of this message have been removed]

            No virus found in this incoming message.
            Checked by AVG.
            Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008
            11:52 AM

            ------------ --------- --------- --------- --------- --------- -

            No virus found in this incoming message.
            Checked by AVG.
            Version: 7.5.524 / Virus Database: 270.4.1/1511 - Release Date: 20/06/2008 11:52 AM

            [Non-text portions of this message have been removed]















            [Non-text portions of this message have been removed]
          • rdoerr@bizserve.com
            I agree that you ll also need a current limiting resistor and I suppose I should have mentioned that as well. Since I haven t seen the schematic that he is
            Message 5 of 11 , Sep 16, 2008
            • 0 Attachment
              I agree that you'll also need a current limiting
              resistor and I suppose I should have mentioned that
              as well. Since I haven't seen the schematic that he
              is working with I suggested that he should do some
              searches to find examples on how it would be implemented.

              I just wanted to bring up that zeners can be used to
              limit the voltage (under the proper implementation)
              and get people thinking of alternate ways to look at
              the over voltage issue.

              This is something I would think about afterwards.
              First I would isolate the existing power supply and
              try a stable 5V supply on the bench. Get the system
              working and stable first then look at other issues.

              Robert



              ------- Original Message -------
              From : Raymond Siminas[mailto:lb_tiger39208@...]
              Sent : 9/16/2008 9:01:37 PM
              To : cosmacelf@yahoogroups.com
              Cc :
              Subject : RE: [cosmacelf] Voltage Tolerant xproms

              Connecting a zener diode directly across the power
              supply is NOT a good idea. If the power supply
              reaches the zener diode voltage. when the zener
              breaks down (it's normal reaction), the power supply
              may see a very low resistance and go into overcurrent
              mode. If it does, there's a good chance that the
              zener diode many be destroyed in the process. Zener
              diodes should have a series resistor chosen to drop
              the voltage applied to it minue the zener diode
              voltage and be rated to daw about 1/10 the current
              (if memory serves) that the zener draws at full
              rating. This is to bias the zener diode to provide
              it's rated voltage under no load conditions. The
              power rating of the series resistor should be chosen
              such that the maximum current that will flow through
              it times the voltage being dropped across it, equals
              the power rating. It's a good idea to go up to the
              next wattage rating just for the sake of a little
              geadroom..







              --- On Tue, 9/16/08, rdoerr@...
              <rdoerr@...> wrote:

              From: rdoerr@... <rdoerr@...>
              Subject: RE: [cosmacelf] Voltage Tolerant xproms
              To: cosmacelf@yahoogroups.com
              Date: Tuesday, September 16, 2008, 5:47 PM






              Have you thought about adding a 5.1v Zener across the
              power supply to help limit the voltage to about 5.1V?
              I've seen that trick used to help limit the over
              voltage on battery operated systems.

              Some google searches about zener diode voltage
              regulation may turn up some example schematics.

              In regards to the "flakyness" have you been able to
              determine if it acts fine at a solid 5V but not at a
              higher voltage like 6V? Can you hook up the system
              to a nice regulated 5V bench supply to verify it
              works ok there? At least that way you can point to
              power being a possible problem.

              Just a couple things to check.

              Robert

              ------- Original Message -------
              From : Bill Rowe[ mailto:bill_rowe@rogers. com]
              Sent : 9/16/2008 7:50:56 PM
              To : cosmacelf@yahoogrou ps.com
              Cc :
              Subject : RE: [cosmacelf] Voltage Tolerant xproms

              working with the MSI/88e I find that its VCC can be
              anywhere from 4.5V to over 6V depending on the state
              of the batteries. It works fine with its own ROM but
              I'm getting way flaky results with my eeproms which
              want 4.5-5V and seem quite sticky about it(at least
              I'm hoping this is what's behind the flakiness).

              I looked at 2764s and they also say 5V plus or minus
              10%. Anybody know of a more tolerant alternative?
              It's easier for me to be sure of >5V than less.

              ----- Original Message -----
              From: Bill Rowe
              To: cosmacelf@yahoogrou ps.com
              Sent: Monday, June 23, 2008 8:09 AM
              Subject: [cosmacelf] MSI88/e Running the IDIOT/4
              Monitor

              As of this morning I have the idiot/4 monitor
              running in the MSI/88e - can
              you say woohoo!

              I need to get a better serial connection going now
              so i can start exploring
              the hardware. The picture below shows my moment of
              victory with the
              semi-eviscerated MSI box connected to my laptop via
              the arduino breadboard.
              If you have very tiny eyes you can make out the
              idiot/4 prompt on the laptop
              screen amid all the debug clutter.

              Again, woohoo! Thanks again to dave for sending me
              the 88e and to lee and
              others for their work on the cpu schematic.

              http://groups. yahoo.com/ group/cosmacelf/
              files/MSI88CPU/ MSI_IDIOT. jpg

              ----- Original Message -----
              From: Bill Rowe
              To: cosmacelf@yahoogrou ps.com
              Sent: Sunday, June 22, 2008 7:37 PM
              Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

              thanks lee. The version of idiot/4 that i'm working
              with is 1K with the
              register saving routines built in and it finds its
              own ram.

              I don't have it working in the MSI/88e yet but i'm
              getting there. I'm at a
              point now where I know it's running and waiting for
              a serial input - won't
              be long now.
              ----- Original Message -----
              From: Lee Hart
              To: cosmacelf@yahoogrou ps.com
              Sent: Sunday, June 22, 2008 3:08 PM
              Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

              randy129 wrote:
              >>> I assembled the TMSI BASIC source, configured
              for 8K ROM
              >>> (PAGE=2000H)

              bill rowe wrote:
              >> This is too funny, I'm in a time warp loop back
              to where Dave was
              >> five years ago - hope I have better luck! I can
              see one thing that
              >> might have been wrong if the idiot monitor
              assumed RAM at 2000.
              >> There may be ram there but it might well cause
              an address conflict
              >> with an eeprom.

              > I thought you said the RAM in yours was at 8000?
              > I don't see the unassembled source for either the
              plain
              > IDIOT, or the combo with tiny basic. Seems like
              it would
              > be a lot of work to convert the listing back to
              plain source.
              > dfnr2 says he assembled it, maybe he still has
              the source?

              It's been a long time; but if I remember correctly
              the IDIOT monitor
              itself doesn't need any RAM at all, and can be
              located anywhere in
              memory that you have 512 bytes available.

              When you add BASIC and the register save/restore
              features, then it needs
              RAM; and it will therefore need to be assembled
              accordingly (and have
              RAM at the intended locations). I think I set it up
              so a 4K ROM could
              have the IDIOT monitor and BASIC, and would occupy
              addresses 0-1FFF. The
              RAM would then start at 2000h (just above this ROM)
              and could go as high
              as you liked.

              --
              Ring the bells that still can ring
              Forget the perfect offering
              There is a crack in everything
              That's how the light gets in -- Leonard Cohen
              --
              Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
              leeahart_at_ earthlink. net

              ------------ --------- --------- --------- ---------
              --------- -

              No virus found in this incoming message.
              Checked by AVG.
              Version: 7.5.524 / Virus Database: 270.4.1/1511 -
              Release Date: 20/06/2008
              11:52 AM

              [Non-text portions of this message have been removed]

              No virus found in this incoming message.
              Checked by AVG.
              Version: 7.5.524 / Virus Database: 270.4.1/1511 -
              Release Date: 20/06/2008
              11:52 AM

              ------------ --------- --------- --------- ---------
              --------- -

              No virus found in this incoming message.
              Checked by AVG.
              Version: 7.5.524 / Virus Database: 270.4.1/1511 -
              Release Date: 20/06/2008 11:52 AM

              [Non-text portions of this message have been removed]

              ------------ --------- --------- ------

              ============ ========= ========= ========= =========
              ========
              Visit the COSMAC ELF website at
              http://www.cosmacel f.comYahoo! Groups Links















              [Non-text portions of this message have been removed]


              ------------------------------------

              ========================================================
              Visit the COSMAC ELF website at
              http://www.cosmacelf.comYahoo! Groups Links
            • Lee Hart
              ... At TMSI, we used National Semiconductor 27C16 and 27C32 CMOS EPROMs. Though spec d for 5v +/- 5%, they actually worked reliably from 4v to 6v. The main
              Message 6 of 11 , Sep 16, 2008
              • 0 Attachment
                Bill Rowe wrote:
                > working with the MSI/88e I find that its VCC can be anywhere from
                > 4.5V to over 6V depending on the state of the batteries. It works
                > fine with its own ROM but I'm getting way flaky results with my
                > eeproms which want 4.5-5V and seem quite sticky about it(at least I'm
                > hoping this is what's behind the flakiness).
                >
                > I looked at 2764s and they also say 5V plus or minus 10%. Anybody
                > know of a more tolerant alternative? It's easier for me to be sure
                > of >5V than less.

                At TMSI, we used National Semiconductor 27C16 and 27C32 CMOS EPROMs.
                Though spec'd for 5v +/- 5%, they actually worked reliably from 4v to
                6v. The main thing that happened at lower supply voltages was that their
                access time got slower.

                --
                Ring the bells that still can ring
                Forget the perfect offering
                There is a crack in everything
                That's how the light gets in -- Leonard Cohen
                --
                Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
              • Raymond Siminas
                Agreed.   I ve been using various types of voltage ragulators since my early days with vacuum tubes (remember the 0V2), and really haven t used zener diodes
                Message 7 of 11 , Sep 16, 2008
                • 0 Attachment
                  Agreed.   I've been using various types of voltage ragulators since my early days with vacuum tubes (remember the 0V2), and really haven't used zener diodes much since the three terminal regulators became popular.  A regulator wins over a zener diode hands down every time :).  Besides, high power zener diodes can get very expensive, and besides, a three terminal regulator works much better.  I'm still a big fan of the LM323K!


                   




                  --- On Tue, 9/16/08, rdoerr@... <rdoerr@...> wrote:

                  From: rdoerr@... <rdoerr@...>
                  Subject: RE: [cosmacelf] Voltage Tolerant xproms
                  To: cosmacelf@yahoogroups.com
                  Date: Tuesday, September 16, 2008, 6:15 PM






                  I agree that you'll also need a current limiting
                  resistor and I suppose I should have mentioned that
                  as well. Since I haven't seen the schematic that he
                  is working with I suggested that he should do some
                  searches to find examples on how it would be implemented.

                  I just wanted to bring up that zeners can be used to
                  limit the voltage (under the proper implementation)
                  and get people thinking of alternate ways to look at
                  the over voltage issue.

                  This is something I would think about afterwards.
                  First I would isolate the existing power supply and
                  try a stable 5V supply on the bench. Get the system
                  working and stable first then look at other issues.

                  Robert

                  ------- Original Message -------
                  From : Raymond Siminas[mailto:lb_tiger39208@ yahoo.com]
                  Sent : 9/16/2008 9:01:37 PM
                  To : cosmacelf@yahoogrou ps.com
                  Cc :
                  Subject : RE: [cosmacelf] Voltage Tolerant xproms

                  Connecting a zener diode directly across the power
                  supply is NOT a good idea. If the power supply
                  reaches the zener diode voltage. when the zener
                  breaks down (it's normal reaction), the power supply
                  may see a very low resistance and go into overcurrent
                  mode. If it does, there's a good chance that the
                  zener diode many be destroyed in the process. Zener
                  diodes should have a series resistor chosen to drop
                  the voltage applied to it minue the zener diode
                  voltage and be rated to daw about 1/10 the current
                  (if memory serves) that the zener draws at full
                  rating. This is to bias the zener diode to provide
                  it's rated voltage under no load conditions. The
                  power rating of the series resistor should be chosen
                  such that the maximum current that will flow through
                  it times the voltage being dropped across it, equals
                  the power rating. It's a good idea to go up to the
                  next wattage rating just for the sake of a little
                  geadroom..

                  --- On Tue, 9/16/08, rdoerr@bizserve. com
                  <rdoerr@bizserve. com> wrote:

                  From: rdoerr@bizserve. com <rdoerr@bizserve. com>
                  Subject: RE: [cosmacelf] Voltage Tolerant xproms
                  To: cosmacelf@yahoogrou ps.com
                  Date: Tuesday, September 16, 2008, 5:47 PM

                  Have you thought about adding a 5.1v Zener across the
                  power supply to help limit the voltage to about 5.1V?
                  I've seen that trick used to help limit the over
                  voltage on battery operated systems.

                  Some google searches about zener diode voltage
                  regulation may turn up some example schematics.

                  In regards to the "flakyness" have you been able to
                  determine if it acts fine at a solid 5V but not at a
                  higher voltage like 6V? Can you hook up the system
                  to a nice regulated 5V bench supply to verify it
                  works ok there? At least that way you can point to
                  power being a possible problem.

                  Just a couple things to check.

                  Robert

                  ------- Original Message -------
                  From : Bill Rowe[ mailto:bill_ rowe@rogers. com]
                  Sent : 9/16/2008 7:50:56 PM
                  To : cosmacelf@yahoogrou ps.com
                  Cc :
                  Subject : RE: [cosmacelf] Voltage Tolerant xproms

                  working with the MSI/88e I find that its VCC can be
                  anywhere from 4.5V to over 6V depending on the state
                  of the batteries. It works fine with its own ROM but
                  I'm getting way flaky results with my eeproms which
                  want 4.5-5V and seem quite sticky about it(at least
                  I'm hoping this is what's behind the flakiness).

                  I looked at 2764s and they also say 5V plus or minus
                  10%. Anybody know of a more tolerant alternative?
                  It's easier for me to be sure of >5V than less.

                  ----- Original Message -----
                  From: Bill Rowe
                  To: cosmacelf@yahoogrou ps.com
                  Sent: Monday, June 23, 2008 8:09 AM
                  Subject: [cosmacelf] MSI88/e Running the IDIOT/4
                  Monitor

                  As of this morning I have the idiot/4 monitor
                  running in the MSI/88e - can
                  you say woohoo!

                  I need to get a better serial connection going now
                  so i can start exploring
                  the hardware. The picture below shows my moment of
                  victory with the
                  semi-eviscerated MSI box connected to my laptop via
                  the arduino breadboard.
                  If you have very tiny eyes you can make out the
                  idiot/4 prompt on the laptop
                  screen amid all the debug clutter.

                  Again, woohoo! Thanks again to dave for sending me
                  the 88e and to lee and
                  others for their work on the cpu schematic.

                  http://groups. yahoo.com/ group/cosmacelf/
                  files/MSI88CPU/ MSI_IDIOT. jpg

                  ----- Original Message -----
                  From: Bill Rowe
                  To: cosmacelf@yahoogrou ps.com
                  Sent: Sunday, June 22, 2008 7:37 PM
                  Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

                  thanks lee. The version of idiot/4 that i'm working
                  with is 1K with the
                  register saving routines built in and it finds its
                  own ram.

                  I don't have it working in the MSI/88e yet but i'm
                  getting there. I'm at a
                  point now where I know it's running and waiting for
                  a serial input - won't
                  be long now.
                  ----- Original Message -----
                  From: Lee Hart
                  To: cosmacelf@yahoogrou ps.com
                  Sent: Sunday, June 22, 2008 3:08 PM
                  Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

                  randy129 wrote:
                  >>> I assembled the TMSI BASIC source, configured
                  for 8K ROM
                  >>> (PAGE=2000H)

                  bill rowe wrote:
                  >> This is too funny, I'm in a time warp loop back
                  to where Dave was
                  >> five years ago - hope I have better luck! I can
                  see one thing that
                  >> might have been wrong if the idiot monitor
                  assumed RAM at 2000.
                  >> There may be ram there but it might well cause
                  an address conflict
                  >> with an eeprom.

                  > I thought you said the RAM in yours was at 8000?
                  > I don't see the unassembled source for either the
                  plain
                  > IDIOT, or the combo with tiny basic. Seems like
                  it would
                  > be a lot of work to convert the listing back to
                  plain source.
                  > dfnr2 says he assembled it, maybe he still has
                  the source?

                  It's been a long time; but if I remember correctly
                  the IDIOT monitor
                  itself doesn't need any RAM at all, and can be
                  located anywhere in
                  memory that you have 512 bytes available.

                  When you add BASIC and the register save/restore
                  features, then it needs
                  RAM; and it will therefore need to be assembled
                  accordingly (and have
                  RAM at the intended locations). I think I set it up
                  so a 4K ROM could
                  have the IDIOT monitor and BASIC, and would occupy
                  addresses 0-1FFF. The
                  RAM would then start at 2000h (just above this ROM)
                  and could go as high
                  as you liked.

                  --
                  Ring the bells that still can ring
                  Forget the perfect offering
                  There is a crack in everything
                  That's how the light gets in -- Leonard Cohen
                  --
                  Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
                  leeahart_at_ earthlink. net

                  ------------ --------- --------- --------- ---------
                  --------- -

                  No virus found in this incoming message.
                  Checked by AVG.
                  Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                  Release Date: 20/06/2008
                  11:52 AM

                  [Non-text portions of this message have been removed]

                  No virus found in this incoming message.
                  Checked by AVG.
                  Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                  Release Date: 20/06/2008
                  11:52 AM

                  ------------ --------- --------- --------- ---------
                  --------- -

                  No virus found in this incoming message.
                  Checked by AVG.
                  Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                  Release Date: 20/06/2008 11:52 AM

                  [Non-text portions of this message have been removed]

                  ------------ --------- --------- ------

                  ============ ========= ========= ========= =========
                  ========
                  Visit the COSMAC ELF website at
                  http://www.cosmacel f.comYahoo! Groups Links

                  [Non-text portions of this message have been removed]

                  ------------ --------- --------- ------

                  ============ ========= ========= ========= ========= ========
                  Visit the COSMAC ELF website at
                  http://www.cosmacel f.comYahoo! Groups Links















                  [Non-text portions of this message have been removed]
                • Bill Rowe
                  The MSI/88e is a fully integrated handheld with its power supply on the CPU board. I don’t think I could bypass it – maybe replace the batteries with a 6v
                  Message 8 of 11 , Sep 16, 2008
                  • 0 Attachment
                    The MSI/88e is a fully integrated handheld with its power supply on the CPU board. I don’t think I could bypass it – maybe replace the batteries with a 6v regulated supply though – that might work. You can see the power arrangement in the bottom left corner of the schematic at http://groups.yahoo.com/group/cosmacelf/files/MSI88CPU/MSI88CPU.PDF It’s complicated with a battery backup and a provision for the 1802 to turn itself off.



                    Lee mentioned the 27C16 and 27C32 I’ll see if I can source and program a 27Cxx. For the moment I have one last new 28C64 and I’m going to start over with it being careful not to let the voltage get much above 5V.



                    Thanks for the suggestions.

                    ----- Original Message -----
                    From: rdoerr@...
                    To: cosmacelf@yahoogroups.com
                    Sent: Tuesday, September 16, 2008 9:15 PM
                    Subject: RE: [cosmacelf] Voltage Tolerant xproms


                    I agree that you'll also need a current limiting
                    resistor and I suppose I should have mentioned that
                    as well. Since I haven't seen the schematic that he
                    is working with I suggested that he should do some
                    searches to find examples on how it would be implemented.

                    I just wanted to bring up that zeners can be used to
                    limit the voltage (under the proper implementation)
                    and get people thinking of alternate ways to look at
                    the over voltage issue.

                    This is something I would think about afterwards.
                    First I would isolate the existing power supply and
                    try a stable 5V supply on the bench. Get the system
                    working and stable first then look at other issues.

                    Robert

                    ------- Original Message -------
                    From : Raymond Siminas[mailto:lb_tiger39208@...]
                    Sent : 9/16/2008 9:01:37 PM
                    To : cosmacelf@yahoogroups.com
                    Cc :
                    Subject : RE: [cosmacelf] Voltage Tolerant xproms

                    Connecting a zener diode directly across the power
                    supply is NOT a good idea. If the power supply
                    reaches the zener diode voltage. when the zener
                    breaks down (it's normal reaction), the power supply
                    may see a very low resistance and go into overcurrent
                    mode. If it does, there's a good chance that the
                    zener diode many be destroyed in the process. Zener
                    diodes should have a series resistor chosen to drop
                    the voltage applied to it minue the zener diode
                    voltage and be rated to daw about 1/10 the current
                    (if memory serves) that the zener draws at full
                    rating. This is to bias the zener diode to provide
                    it's rated voltage under no load conditions. The
                    power rating of the series resistor should be chosen
                    such that the maximum current that will flow through
                    it times the voltage being dropped across it, equals
                    the power rating. It's a good idea to go up to the
                    next wattage rating just for the sake of a little
                    geadroom..

                    --- On Tue, 9/16/08, rdoerr@...
                    <rdoerr@...> wrote:

                    From: rdoerr@... <rdoerr@...>
                    Subject: RE: [cosmacelf] Voltage Tolerant xproms
                    To: cosmacelf@yahoogroups.com
                    Date: Tuesday, September 16, 2008, 5:47 PM

                    Have you thought about adding a 5.1v Zener across the
                    power supply to help limit the voltage to about 5.1V?
                    I've seen that trick used to help limit the over
                    voltage on battery operated systems.

                    Some google searches about zener diode voltage
                    regulation may turn up some example schematics.

                    In regards to the "flakyness" have you been able to
                    determine if it acts fine at a solid 5V but not at a
                    higher voltage like 6V? Can you hook up the system
                    to a nice regulated 5V bench supply to verify it
                    works ok there? At least that way you can point to
                    power being a possible problem.

                    Just a couple things to check.

                    Robert

                    ------- Original Message -------
                    From : Bill Rowe[ mailto:bill_rowe@rogers. com]
                    Sent : 9/16/2008 7:50:56 PM
                    To : cosmacelf@yahoogrou ps.com
                    Cc :
                    Subject : RE: [cosmacelf] Voltage Tolerant xproms

                    working with the MSI/88e I find that its VCC can be
                    anywhere from 4.5V to over 6V depending on the state
                    of the batteries. It works fine with its own ROM but
                    I'm getting way flaky results with my eeproms which
                    want 4.5-5V and seem quite sticky about it(at least
                    I'm hoping this is what's behind the flakiness).

                    I looked at 2764s and they also say 5V plus or minus
                    10%. Anybody know of a more tolerant alternative?
                    It's easier for me to be sure of >5V than less.

                    ----- Original Message -----
                    From: Bill Rowe
                    To: cosmacelf@yahoogrou ps.com
                    Sent: Monday, June 23, 2008 8:09 AM
                    Subject: [cosmacelf] MSI88/e Running the IDIOT/4
                    Monitor

                    As of this morning I have the idiot/4 monitor
                    running in the MSI/88e - can
                    you say woohoo!

                    I need to get a better serial connection going now
                    so i can start exploring
                    the hardware. The picture below shows my moment of
                    victory with the
                    semi-eviscerated MSI box connected to my laptop via
                    the arduino breadboard.
                    If you have very tiny eyes you can make out the
                    idiot/4 prompt on the laptop
                    screen amid all the debug clutter.

                    Again, woohoo! Thanks again to dave for sending me
                    the 88e and to lee and
                    others for their work on the cpu schematic.

                    http://groups. yahoo.com/ group/cosmacelf/
                    files/MSI88CPU/ MSI_IDIOT. jpg

                    ----- Original Message -----
                    From: Bill Rowe
                    To: cosmacelf@yahoogrou ps.com
                    Sent: Sunday, June 22, 2008 7:37 PM
                    Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

                    thanks lee. The version of idiot/4 that i'm working
                    with is 1K with the
                    register saving routines built in and it finds its
                    own ram.

                    I don't have it working in the MSI/88e yet but i'm
                    getting there. I'm at a
                    point now where I know it's running and waiting for
                    a serial input - won't
                    be long now.
                    ----- Original Message -----
                    From: Lee Hart
                    To: cosmacelf@yahoogrou ps.com
                    Sent: Sunday, June 22, 2008 3:08 PM
                    Subject: Re: [cosmacelf] Re: Fiddling with MSI88/e

                    randy129 wrote:
                    >>> I assembled the TMSI BASIC source, configured
                    for 8K ROM
                    >>> (PAGE=2000H)

                    bill rowe wrote:
                    >> This is too funny, I'm in a time warp loop back
                    to where Dave was
                    >> five years ago - hope I have better luck! I can
                    see one thing that
                    >> might have been wrong if the idiot monitor
                    assumed RAM at 2000.
                    >> There may be ram there but it might well cause
                    an address conflict
                    >> with an eeprom.

                    > I thought you said the RAM in yours was at 8000?
                    > I don't see the unassembled source for either the
                    plain
                    > IDIOT, or the combo with tiny basic. Seems like
                    it would
                    > be a lot of work to convert the listing back to
                    plain source.
                    > dfnr2 says he assembled it, maybe he still has
                    the source?

                    It's been a long time; but if I remember correctly
                    the IDIOT monitor
                    itself doesn't need any RAM at all, and can be
                    located anywhere in
                    memory that you have 512 bytes available.

                    When you add BASIC and the register save/restore
                    features, then it needs
                    RAM; and it will therefore need to be assembled
                    accordingly (and have
                    RAM at the intended locations). I think I set it up
                    so a 4K ROM could
                    have the IDIOT monitor and BASIC, and would occupy
                    addresses 0-1FFF. The
                    RAM would then start at 2000h (just above this ROM)
                    and could go as high
                    as you liked.

                    --
                    Ring the bells that still can ring
                    Forget the perfect offering
                    There is a crack in everything
                    That's how the light gets in -- Leonard Cohen
                    --
                    Lee A. Hart, 814 8th Ave N, Sartell MN 56377,
                    leeahart_at_ earthlink. net

                    ------------ --------- --------- --------- ---------
                    --------- -

                    No virus found in this incoming message.
                    Checked by AVG.
                    Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                    Release Date: 20/06/2008
                    11:52 AM

                    [Non-text portions of this message have been removed]

                    No virus found in this incoming message.
                    Checked by AVG.
                    Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                    Release Date: 20/06/2008
                    11:52 AM

                    ------------ --------- --------- --------- ---------
                    --------- -

                    No virus found in this incoming message.
                    Checked by AVG.
                    Version: 7.5.524 / Virus Database: 270.4.1/1511 -
                    Release Date: 20/06/2008 11:52 AM

                    [Non-text portions of this message have been removed]

                    ------------ --------- --------- ------

                    ============ ========= ========= ========= =========
                    ========
                    Visit the COSMAC ELF website at
                    http://www.cosmacel f.comYahoo! Groups Links

                    [Non-text portions of this message have been removed]

                    ------------------------------------

                    ========================================================
                    Visit the COSMAC ELF website at
                    http://www.cosmacelf.comYahoo! Groups Links






                    ------------------------------------------------------------------------------


                    No virus found in this incoming message.
                    Checked by AVG.
                    Version: 7.5.524 / Virus Database: 270.6.21/1674 - Release Date: 16/09/2008 8:15 AM


                    [Non-text portions of this message have been removed]
                  • Lee Hart
                    ... I think the power supply is just the raw unregulated battery voltage. There is a transistor that simply turns on to connect the battery to VCC. Alkaline
                    Message 9 of 11 , Sep 16, 2008
                    • 0 Attachment
                      Bill Rowe wrote:
                      > The MSI/88e is a fully integrated handheld with its power supply on
                      > the CPU board. I don’t think I could bypass it – maybe replace the
                      > batteries with a 6v regulated supply though – that might work. You
                      > can see the power arrangement in the bottom left corner of the
                      > schematic at
                      > http://groups.yahoo.com/group/cosmacelf/files/MSI88CPU/MSI88CPU.PDF
                      > It’s complicated with a battery backup and a provision for the 1802
                      > to turn itself off.

                      I think the "power supply" is just the raw unregulated battery voltage.
                      There is a transistor that simply turns on to connect the battery to
                      VCC. Alkaline AA cells range from about 1.0v (dead) to 1.62v (new and
                      fresh). With just that saturated transistor between batteries and VCC,
                      you get something like 3.9v to 6.38v.

                      Good ol' CMOS is fine with this, but modern parts are more fussy
                      (especially on the high side, since they've shrunk all the chip sizes).

                      One solution is to use nicads instead of alkalines. Nicads will get up
                      to 1.56v while on charge, but fall almost immediately below 1.4v when
                      the charger is unplugged, and 1.35v under any kind of load.

                      Another solution would be to replace the transistor with a low-dropout
                      series pass regulator. It would also need a shutdown pin, so it won't be
                      the simple 3-terminal type.

                      --
                      Ring the bells that still can ring
                      Forget the perfect offering
                      There is a crack in everything
                      That's how the light gets in -- Leonard Cohen
                      --
                      Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
                    • randy129
                      ... I looked at the schematic you mentioned, and I don t claim to totally understand it, but it looks like it may already have a zener based regulator, cr14.
                      Message 10 of 11 , Sep 16, 2008
                      • 0 Attachment
                        --- "Bill Rowe" wrote:
                        >
                        > working with the MSI/88e I find that its VCC can be anywhere from
                        > 4.5V to over 6V depending on the state of the batteries.

                        I looked at the schematic you mentioned, and I don't
                        claim to totally understand it, but it looks like it
                        may already have a zener based regulator, cr14.
                        It says "open" on schematic, which I don't know how to
                        interpret. Does that mean cr14 is missing?

                        Where did you measure the vcc level?

                        I am a tiny bit skeptical that the problem is vcc being too
                        high (but it could be). One very easy way to lower the
                        voltage by 0.7 volts would be to put a normal (non-zener)
                        diode in *series* with the batteries.

                        Almost any diode would probably work, but I would use
                        a 1N4004 for the simple reason that I have a bunch of them!
                        (I am assuming the MSI/88e draws less than 1 amp!)

                        The down side is that the drop would still be present
                        when the batteries are dying.

                        You could put a diode in temporarily at least, and find
                        out if the problem really is excess voltage.

                        I wonder if you could trace the vcc pin from ROM back to
                        power supply circuit (audible continuity checker is quite
                        valuable here) and verify just where it meets up with the
                        power suppy circuit in that lower left hand of schematic.
                        Does ROM supply connect directly to Vbat??? Or does it
                        connect after Q5??? And just what the heck is Q3 doing???

                        Randy
                      • Lee Hart
                        ... Yes; nothing is installed at CR14 in the MSI/88 s that I have. The symbol printed on the PC board identifies it as a zener diode. My guess is that CR14 was
                        Message 11 of 11 , Sep 17, 2008
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                          randy129 wrote:
                          > I looked at the schematic you mentioned, and I don't
                          > claim to totally understand it, but it looks like it
                          > may already have a zener based regulator, cr14.
                          > It says "open" on schematic, which I don't know how to
                          > interpret. Does that mean cr14 is missing?

                          Yes; nothing is installed at CR14 in the MSI/88's that I have. The
                          symbol printed on the PC board identifies it as a zener diode.

                          My guess is that CR14 was installed if you had a rechargeable battery
                          pack, and AC adapter to charge it. They would have picked the zener
                          voltage of CR14 so when the batteries were fully charged, CR14 would
                          conduct, and turn on Q5, and so turn on the unit. This would draw enough
                          current from the AC adapter to keep the batteries from being overcharged.

                          Q5 and CR14 are not wired as a regulator; if that were the case, the
                          transistor would be NPN instead of PNP, and its emitter and collector
                          would be swapped. But if you did this, there would be no way to turn it
                          on/off.

                          > Where did you measure the vcc level?
                          >
                          > I am a tiny bit skeptical that the problem is vcc being too
                          > high (but it could be).

                          Older CMOS parts used a process that had breakdown voltages in the
                          15-25v range. Newer parts have shrunk all the dimensions so they have
                          breakdowns in the 6-8v range (for nominally 5v parts).

                          > One very easy way to lower the voltage by 0.7 volts would be to put
                          > a normal (non-zener) diode in *series* with the batteries.

                          That would work; but it would also shorten battery life because the unit
                          would quit working with 0.7v more voltage in the batteries.

                          > (I am assuming the MSI/88e draws less than 1 amp!)

                          Yes; WAY less than an amp! The LED display takes most of the power.
                          Perhaps 250ma with all segments lit.

                          > Does ROM supply connect directly to Vbat?

                          No; it connects to VCC.

                          > And just what the heck is Q3 doing?

                          My guess is that it's a second way to turn on parts of the unit under
                          software control.
                          --
                          Ring the bells that still can ring
                          Forget the perfect offering
                          There is a crack in everything
                          That's how the light gets in -- Leonard Cohen
                          --
                          Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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