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help with 4K board

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  • glendroger
    I ve just dusted off my ELF after 30 years and I can light up the Q led with the good old Input button and the original program... 7A 3F 00 7B 30 01 I had
    Message 1 of 10 , Jun 26, 2007
      I've just dusted off my ELF after 30 years and I can light up the Q
      led with the good old Input button and the original program...
      7A
      3F 00
      7B
      30 01

      I had scooped some 2102s from my 4K board to get lower case on my
      TRS80 and so it was in rough shape. After adding the 2102s back, I've
      got a problem that some of you bright guys might be able to help me with.

      When I put in the 4K board and enter the above Q led program it enters
      as follows...
      78
      3D 00
      79
      30 01

      When I enter the original program and jam in the 4K board with the
      power on (I know, I know) it reverts to the 78 3D...

      So the 7th bit is being driven low by the 4 k board... so where do I
      look on the 4 K board???

      I've scoured the board but I can't see the fault.

      Thanks.
    • Andrew Wasson
      Hey Glen, Are you running the 4k board with the original 1/4k on your elf. It sounds like you are. I had a heck of a time back in the day getting my 4k ram to
      Message 2 of 10 , Jun 26, 2007
        Hey Glen,
        Are you running the 4k board with the original 1/4k on your elf. It
        sounds like you are. I had a heck of a time back in the day getting my
        4k ram to work with n ELFII and I'm pretty certain I had to remove my
        original ram to make it work.

        * I think you have to do the same thing with the Super Elf... I'll let
        you know when I finish building my Super Expansion Board :-)

        Andrew

        --- In cosmacelf@yahoogroups.com, "glendroger" <groger@...> wrote:
        >
        > I've just dusted off my ELF after 30 years and I can light up the Q
        > led with the good old Input button and the original program...
        > 7A
        > 3F 00
        > 7B
        > 30 01
        >
        > I had scooped some 2102s from my 4K board to get lower case on my
        > TRS80 and so it was in rough shape. After adding the 2102s back, I've
        > got a problem that some of you bright guys might be able to help me
        with.
        >
        > When I put in the 4K board and enter the above Q led program it enters
        > as follows...
        > 78
        > 3D 00
        > 79
        > 30 01
        >
        > When I enter the original program and jam in the 4K board with the
        > power on (I know, I know) it reverts to the 78 3D...
        >
        > So the 7th bit is being driven low by the 4 k board... so where do I
        > look on the 4 K board???
        >
        > I've scoured the board but I can't see the fault.
        >
        > Thanks.
        >
      • Dave Ruske
        Tthe original 256 bytes weren t fully decoded; just the low 8 bits, meaning that the 256 bytes would show up in each page of RAM. Either the chips need to be
        Message 3 of 10 , Jun 27, 2007
          Tthe original 256 bytes weren't fully decoded; just the low 8 bits,
          meaning that the 256 bytes would show up in each page of RAM. Either
          the chips need to be pulled as Andrew suggests, or there's a jumper
          to them that'll only enable them depending on additional decode logic
          from the 4K board. If you have the ELF II schematic, look for a
          jumper related to the chip enable (or some such thing) running from
          pin 17 on the original chips (a chip enable signal, I think) to pin
          69 on the bus connector. The schematic I'm looking at shows this as
          "J1" on the main ELF II board.

          See the ELF II and 4K expansion schematics on:
          <http://groups.msn.com/RCACDP1802CosmacComputer/>

          Good luck!
          Dave

          On Jun 27, 2007, at 1:21 AM, Andrew Wasson wrote:
          > Are you running the 4k board with the original 1/4k on your elf. It
          > sounds like you are. I had a heck of a time back in the day getting my
          > 4k ram to work with n ELFII and I'm pretty certain I had to remove my
          > original ram to make it work.



          [Non-text portions of this message have been removed]
        • timothy_purves
          ... I ve ... with. ... enters ... You need to remove the original ram, unless you configure the board to an address space that doesn t overlap with the onboard
          Message 4 of 10 , Jun 27, 2007
            --- In cosmacelf@yahoogroups.com, "glendroger" <groger@...> wrote:
            >
            > I've just dusted off my ELF after 30 years and I can light up the Q
            > led with the good old Input button and the original program...
            > 7A
            > 3F 00
            > 7B
            > 30 01
            >
            > I had scooped some 2102s from my 4K board to get lower case on my
            > TRS80 and so it was in rough shape. After adding the 2102s back,
            I've
            > got a problem that some of you bright guys might be able to help me
            with.
            >
            > When I put in the 4K board and enter the above Q led program it
            enters
            > as follows...
            > 78
            > 3D 00
            > 79
            > 30 01
            >
            > When I enter the original program and jam in the 4K board with the
            > power on (I know, I know) it reverts to the 78 3D...
            >
            > So the 7th bit is being driven low by the 4 k board... so where do I
            > look on the 4 K board???
            >
            > I've scoured the board but I can't see the fault.
            >
            > Thanks.
            >

            You need to remove the original ram, unless you configure the board
            to an address space that doesn't overlap with the onboard ram.
          • Richard
            on the elf II, the 4k board is suppost to, take over the address space that it is set too. but there is a jumper (J1) on the motherboard that is removed when a
            Message 5 of 10 , Jun 27, 2007
              on the elf II, the 4k board is suppost to, take over the address space that
              it is set too.
              but there is a jumper (J1) on the motherboard that is removed when a 4k
              board is installed.
              and the select signal is from the 4k board Q1

              I would start by removing, A17,25,33,41 and A9 on the 4k board.
              and checking the results, if the High bit is still low, you have a short on
              this the D7(34) line.
              if the result is 7F 3F then add the chips back one at a time to see which is
              locking it low, Starting with A9

              ----- Original Message -----
              From: "glendroger" <groger@...>
              To: <cosmacelf@yahoogroups.com>
              Sent: Wednesday, June 27, 2007 1:08 AM
              Subject: [cosmacelf] help with 4K board


              > I've just dusted off my ELF after 30 years and I can light up the Q
              > led with the good old Input button and the original program...
              > 7A
              > 3F 00
              > 7B
              > 30 01
              >
              > I had scooped some 2102s from my 4K board to get lower case on my
              > TRS80 and so it was in rough shape. After adding the 2102s back, I've
              > got a problem that some of you bright guys might be able to help me with.
              >
              > When I put in the 4K board and enter the above Q led program it enters
              > as follows...
              > 78
              > 3D 00
              > 79
              > 30 01
              >
              > When I enter the original program and jam in the 4K board with the
              > power on (I know, I know) it reverts to the 78 3D...
              >
              > So the 7th bit is being driven low by the 4 k board... so where do I
              > look on the 4 K board???
              >
              > I've scoured the board but I can't see the fault.
              >
              > Thanks.
              >
              >
              >
              > ========================================================
              > Visit the COSMAC ELF website at http://www.cosmacelf.com
              > Yahoo! Groups Links
              >
              >
              >
              >
            • Richard
              Cancel previous tip, After a Re Read of the message I discovered that It is not Bit 7 that is the problem. But Bit 1. 7A = 01111010 78 = 01111000 Bits=76543210
              Message 6 of 10 , Jun 27, 2007
                Cancel previous tip,
                After a Re Read of the message I discovered that It is not Bit 7 that is the
                problem.
                But Bit 1.
                7A = 01111010
                78 = 01111000
                Bits=76543210

                I would start by removing, A11,19,27,35 and A8 on the 4k board.
                and checking the results, if the bit is still low, you have a short on
                this the D1(58) line.
                if the result is 7F 3F then add the chips back one at a time to see which is
                locking it low, Starting with A8

                Richard
              • glendroger
                OK... I ve gone over this with a magnifying glass, tracing everything. I m desparately avoiding desoldering the chips to avoid the mess. I just noticed
                Message 7 of 10 , Jul 7, 2007
                  OK... I've gone over this with a magnifying glass, tracing everything.
                  I'm desparately avoiding desoldering the chips to avoid the mess. I
                  just noticed something new...

                  Press FF and you get FD... for the first 8 times. Then you get FF...
                  for the next 8 times!!! And so on.

                  So
                  00 to 07 - bit D01 is forced low
                  08 to 0F - bit D01 is fine
                  10 to 17 - bit D01 is forced low
                  18 to 1F - bit D01 is fine

                  When I type in C0 FO 00 and try to run the monitor with the 4K board
                  in it won't run so I can't check to see what is happening upwards in
                  memory.

                  Does that make sense to anyone?

                  Thanks!

                  Glen

                  --- In cosmacelf@yahoogroups.com, "Richard" <stateamuse@...> wrote:
                  >
                  > Cancel previous tip,
                  > After a Re Read of the message I discovered that It is not Bit 7
                  that is the
                  > problem.
                  > But Bit 1.
                  > 7A = 01111010
                  > 78 = 01111000
                  > Bits=76543210
                  >
                  > I would start by removing, A11,19,27,35 and A8 on the 4k board.
                  > and checking the results, if the bit is still low, you have a short on
                  > this the D1(58) line.
                  > if the result is 7F 3F then add the chips back one at a time to see
                  which is
                  > locking it low, Starting with A8
                  >
                  > Richard
                  >
                • randy129
                  ... I m not familiar with that particular board, but it sounds like A0 is shorted to D1. Randy
                  Message 8 of 10 , Jul 8, 2007
                    --- "glendroger" <groger@...> wrote:

                    > just noticed something new...
                    >
                    > Press FF and you get FD... for the first 8 times. Then you get FF...
                    > for the next 8 times!!! And so on.

                    I'm not familiar with that particular board, but it
                    sounds like A0 is shorted to D1.

                    Randy
                  • randy129
                    ... oops, I mean A3 shorted to D1. Randy
                    Message 9 of 10 , Jul 8, 2007
                      > I'm not familiar with that particular board, but it
                      > sounds like A0 is shorted to D1.

                      oops, I mean A3 shorted to D1.

                      Randy
                    • Steve Valin
                      Glen, I have seen this on both of my unexpanded ELF II boards. The culprit in my case was a flakey 2101 SRAM. It had a weak driver on one of it s I/O pins. I
                      Message 10 of 10 , Jul 8, 2007
                        Glen,

                        I have seen this on both of my unexpanded ELF II
                        boards. The culprit in my case was a flakey 2101
                        SRAM. It had a weak driver on one of it's I/O pins.
                        I had to use a scope to see what was going on.
                        Basically, when you load a value into the SRAM using
                        the input switch, it will write the value to the SRAM,
                        then turn around and read it back out, which is
                        latched to the displays. I replaced the flakey 2101
                        parts and the problem went away. You could have a bad
                        SRAM. I would try swapping your SRAM around to see if
                        the problem follows the SRAM or stays the same.

                        -steve

                        --- glendroger <groger@...> wrote:

                        > OK... I've gone over this with a magnifying glass,
                        > tracing everything.
                        > I'm desparately avoiding desoldering the chips to
                        > avoid the mess. I
                        > just noticed something new...
                        >
                        > Press FF and you get FD... for the first 8 times.
                        > Then you get FF...
                        > for the next 8 times!!! And so on.
                        >
                        > So
                        > 00 to 07 - bit D01 is forced low
                        > 08 to 0F - bit D01 is fine
                        > 10 to 17 - bit D01 is forced low
                        > 18 to 1F - bit D01 is fine
                        >
                        > When I type in C0 FO 00 and try to run the monitor
                        > with the 4K board
                        > in it won't run so I can't check to see what is
                        > happening upwards in
                        > memory.
                        >
                        > Does that make sense to anyone?
                        >
                        > Thanks!
                        >
                        > Glen
                        >
                        > --- In cosmacelf@yahoogroups.com, "Richard"
                        > <stateamuse@...> wrote:
                        > >
                        > > Cancel previous tip,
                        > > After a Re Read of the message I discovered that
                        > It is not Bit 7
                        > that is the
                        > > problem.
                        > > But Bit 1.
                        > > 7A = 01111010
                        > > 78 = 01111000
                        > > Bits=76543210
                        > >
                        > > I would start by removing, A11,19,27,35 and A8 on
                        > the 4k board.
                        > > and checking the results, if the bit is still low,
                        > you have a short on
                        > > this the D1(58) line.
                        > > if the result is 7F 3F then add the chips back one
                        > at a time to see
                        > which is
                        > > locking it low, Starting with A8
                        > >
                        > > Richard
                        > >
                        >
                        >
                        >



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