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88-2SIO Hardware Handshaking Issues

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  • Tom Sanderson
    I m trying to understand the 88-2SIO RS-232 interface, especially RTS/CTS handshaking. There are some notes in the 2SIO manual that I don t quite understand
    Message 1 of 9 , Jul 3, 2008
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      I'm trying to understand the 88-2SIO RS-232 interface, especially
      RTS/CTS handshaking. There are some notes in the 2SIO manual that I
      don't quite understand and I'm seeing some strange symptoms when
      connecting to a Serial to Ethernet converter.

      I'm testing the connection to the TURMON monitor in an 8800bt. I've
      verified the problem exists with more than one 2SIO plus the Turnkey
      Board I/O.

      The 2SIO and internal cable are in the MITS factory configuration for
      RS-232.

      The 2SIO manual say DTR is required to be "normal" RS-232. The
      standard internal cable does not connect DTR. The manual says RTS can
      be used for DTR. Comments on 2SIO DTR would be helpful.

      I'm connecting to the 2SIO with a flat ribbon cable with all lines
      connected. Communication with the monitor works with an ADM-3a, two
      brands of USB to Serial converter, Hyper Terminal in Windows 2003, and
      Procomm Plus and DOS.

      The connection works with the Serial to Ethernet converter, if I have
      a Break out Box in the circuit. Problems occur if I remove the Break
      out Box. Note that the Break out Box changes RTS from 9.81v to 7.19v.

      I now have three failure modes:

      1) Turmon receives a stream of garbage (echo characters ok);
      2) Turmon doesn't receive input ("." Prompt sent ok);
      3) Turmon often receives incorrect character (good and bad
      characterless echo ok);

      The problem occurs even if handshaking is turned off in Hyper Terminal
      and off in the Ethernet converter.

      I have three ways to make the connection work:

      1) Use Break Out Box with LEDs;
      2) Cut line 4 RTS - No input to Altair;
      3) Cut line 4 RTS and line 5 CTS to Altair and jumper RTS & CTS on the
      GW-312 side.

      I'm learning 2SIO interfacing in general and found the following in
      the manual: NOTICE!! "If the Data Carrier Detect and Clear to Send
      inputs are not connected, they must be jumpered to Ground."

      I also found a handwritten note: "MITS manual was unclear in it's note
      to jumper DCD & CTS to GND. These signals must be jumpered to +5v at
      the interface connector because it gets inverted before it gets to the
      6850.

      Any comments on these statements would be helpful. Turmon may not need
      handshaking and I have a workaround for this issue. I assume hardware
      handshaking is useful and I will eventually need it. I'm trying to
      understand my current issue and learn about configuration of CTS, RTS,
      CD, and DTR for the 2SIO.

      Does anyone in the group have 2SIO manual clarifications or RS-232
      knowledge to share?

      Mote: My RS-232 book has the following bit of Altair history:

      "Nothing in the world of microcomputers is more reviled, despised, or
      misunderstood that the RS-232-C interface. Ordinary mild-mannered
      humans are driven berserk by the experience of connecting their
      computer equipment. Sometimes this rage gets out of hand:"

      "A dispute between a customer and a computer store over a $180 bill
      has ended in tragedy with the fatal shooting of the store's owner.

      A 42-year-old man, Floyd French of Gladstone, Missouri, was arrested
      at the scene and later charged with first-degree murder. The victim
      was the owner of the Altair Computer Center, Henry Phillip Bouldin.
      According to police, French had bought a computer from Bouldin, then
      brought in a printer purchased elsewhere and asked that [the store]
      make the two compatible..."
      -- Infoworld, June 20, 1983.


      Tom
    • jack99rubin
      ... or ... Thanks Tom - I ve got nothing to add to that!! Have a great holiday weekend, all ye who lurk. Jack
      Message 2 of 9 , Jul 3, 2008
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        >
        > Mote: My RS-232 book has the following bit of Altair history:
        >
        > "Nothing in the world of microcomputers is more reviled, despised,
        or
        > misunderstood that the RS-232-C interface. Ordinary mild-mannered
        > humans are driven berserk by the experience of connecting their
        > computer equipment. Sometimes this rage gets out of hand:"
        >
        > "A dispute between a customer and a computer store over a $180 bill
        > has ended in tragedy with the fatal shooting of the store's owner.
        >
        > A 42-year-old man, Floyd French of Gladstone, Missouri, was arrested
        > at the scene and later charged with first-degree murder. The victim
        > was the owner of the Altair Computer Center, Henry Phillip Bouldin.
        > According to police, French had bought a computer from Bouldin, then
        > brought in a printer purchased elsewhere and asked that [the store]
        > make the two compatible..."
        > -- Infoworld, June 20, 1983.
        >

        Thanks Tom - I've got nothing to add to that!!
        Have a great holiday weekend, all ye who lurk.

        Jack
      • Alan Outhier
        OH! One of my hot buttons, I ll try to keep it short & simple. Hopefully, both devices are configured as DTEs (neither is a modem), and both devices are
        Message 3 of 9 , Jul 3, 2008
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          OH! One of my hot buttons, I'll try to keep it short & simple.

          Hopefully, both devices are configured as DTEs (neither is a modem),
          and both devices are equipped with male db25s (part of being
          configured as a DTE but some manufactures never understood that).

          Option 1 - buy a commercial null modem cable.

          Option 2 - build your own.
          pin 2 -> pin 3
          pin 3 -> pin 2
          pin 7 -> pin 7

          At each end jumper pins 6-8-20 ('hope I remember this correctly).

          Don' t try to implement hardware control, it won't buy you anything.

          There's two cents worth for free!

          Al


          At 01:07 PM 7/3/2008, jack99rubin wrote:

          > >
          > > Mote: My RS-232 book has the following bit of Altair history:
          > >
          > > "Nothing in the world of microcomputers is more reviled, despised,
          >or
          > > misunderstood that the RS-232-C interface. Ordinary mild-mannered
          > > humans are driven berserk by the experience of connecting their
          > > computer equipment. Sometimes this rage gets out of hand:"
          > >
          > > "A dispute between a customer and a computer store over a $180 bill
          > > has ended in tragedy with the fatal shooting of the store's owner.
          > >
          > > A 42-year-old man, Floyd French of Gladstone, Missouri, was arrested
          > > at the scene and later charged with first-degree murder. The victim
          > > was the owner of the Altair Computer Center, Henry Phillip Bouldin.
          > > According to police, French had bought a computer from Bouldin, then
          > > brought in a printer purchased elsewhere and asked that [the store]
          > > make the two compatible..."
          > > -- Infoworld, June 20, 1983.
          > >
          >
          >Thanks Tom - I've got nothing to add to that!!
          >Have a great holiday weekend, all ye who lurk.
          >
          >Jack
          >
          >
          >------------------------------------
          >
          >Yahoo! Groups Links
          >
          >
          >
        • Tom Sanderson
          ... I think this likely good advice, but since learning is part of the fun, I m trying to better understand handshaking and why it won t buy me anything. I m
          Message 4 of 9 , Jul 4, 2008
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            > Don' t try to implement hardware control, it won't buy you anything.

            I think this likely good advice, but since learning is part of the
            fun, I'm trying to better understand handshaking and why it won't buy
            me anything. I'm curious about the handshaking signals provided by
            the 2SIO and the short notes in the manual about some signals.

            I'm also curious about the effect of the Break Out Box LEDs on the
            symptoms. Even if I do not use hardware control, I need to learn how
            to use the Serial to Ethernet converter. The converter does seem to
            require CTS, but does not like RTS from the 2SIO. It is happy when
            CTS is not connected to the 2SIO.

            > Hopefully, both devices are configured as DTEs (neither is a
            modem),
            > and both devices are equipped with male db25s (part of being
            > configured as a DTE but some manufactures never understood that).

            The Ethernet converter is DTE and uses a 9-pin male connector. The
            2SIO is DCE and uses the proper female db25. I can work around the
            issue, but am still looking for a better understanding of the 2SIO
            CTS and the manual note about using it for DTR.

            I'd like to learn more about the following:

            ...found the following in
            the manual: NOTICE!! "If the Data Carrier Detect and Clear to Send
            inputs are not connected, they must be jumpered to Ground."

            I also found a handwritten note: "MITS manual was unclear in it's note
            to jumper DCD & CTS to GND. These signals must be jumpered to +5v at
            the interface connector because it gets inverted before it gets to the
            6850.

            Tom

            -- In altaircomputerclub@yahoogroups.com, Alan Outhier <aouthier@...>
            wrote:
            >
            > OH! One of my hot buttons, I'll try to keep it short & simple.
            >
            > Hopefully, both devices are configured as DTEs (neither is a
            modem),
            > and both devices are equipped with male db25s (part of being
            > configured as a DTE but some manufactures never understood that).
            >
            > Option 1 - buy a commercial null modem cable.
            >
            > Option 2 - build your own.
            > pin 2 -> pin 3
            > pin 3 -> pin 2
            > pin 7 -> pin 7
            >
            > At each end jumper pins 6-8-20 ('hope I remember this
            correctly).
            >
            > Don' t try to implement hardware control, it won't buy you anything.
            >
            > There's two cents worth for free!
            >
            > Al
            >
            >
            > At 01:07 PM 7/3/2008, jack99rubin wrote:
            >
            > > >
            > > > Mote: My RS-232 book has the following bit of Altair history:
            > > >
            > > > "Nothing in the world of microcomputers is more reviled,
            despised,
            > >or
            > > > misunderstood that the RS-232-C interface. Ordinary mild-
            mannered
            > > > humans are driven berserk by the experience of connecting their
            > > > computer equipment. Sometimes this rage gets out of hand:"
            > > >
            > > > "A dispute between a customer and a computer store over a $180
            bill
            > > > has ended in tragedy with the fatal shooting of the store's
            owner.
            > > >
            > > > A 42-year-old man, Floyd French of Gladstone, Missouri, was
            arrested
            > > > at the scene and later charged with first-degree murder. The
            victim
            > > > was the owner of the Altair Computer Center, Henry Phillip
            Bouldin.
            > > > According to police, French had bought a computer from Bouldin,
            then
            > > > brought in a printer purchased elsewhere and asked that [the
            store]
            > > > make the two compatible..."
            > > > -- Infoworld, June 20, 1983.
            > > >
            > >
            > >Thanks Tom - I've got nothing to add to that!!
            > >Have a great holiday weekend, all ye who lurk.
            > >
            > >Jack
            > >
            > >
            > >------------------------------------
            > >
            > >Yahoo! Groups Links
            > >
            > >
            > >
            >
          • Dan Roganti
            Tom Sanderson wrote: I m trying to understand the 88-2SIO RS-232 interface, especially RTS/CTS handshaking. There are some notes in the 2SIO manual that I
            Message 5 of 9 , Jul 4, 2008
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              Tom Sanderson wrote:
              I'm trying to understand the 88-2SIO RS-232 interface, especially
              RTS/CTS handshaking. There are some notes in the 2SIO manual that I
              don't quite understand and I'm seeing some strange symptoms when
              connecting to a Serial to Ethernet converter.
                
              This has always been a stickler
              Over the years, these are some things that I keep in mind and helps avoid the racking ones brains out :)
              I always pass it on wherever I go.
              (you'll find this in the various references to RS232)

              --There's only 6 kinds of combinations for RS232 cables--I used to memorize this.
              1. DTE - DTE: w/ Handshaking (signals always cross)
              2. DTE - DTE: w/ No Handshaking (loopback all handshake lines)
              3. DTE - DCE w/Handshaking (signals never cross)
              4. DTE - DCE w/No Handshaking (loopback all handshake lines)
              5. DTE - Peripheral:  such as a printer,papertape--still a DTE ,but Dumb Terminal Equip :)
                                 This is where your info on CTS<-->DTR comes from
              6. Loopback tester -- this is a given

              --Hardware Handshaking are always software controlled, when it doubt, loop it back.
              Unless you have specific info from the docs explaining the timing of these signals, it's best to loopback them
              This helps prevent the software from getting confused :)
              This is wired on both ends --and always both sets, not just one set
              RTS<-->CTS
              DTR<-->DCD<-->DSR
              --DCE is only to communicate over a transport medium, such as, a phone line, T1 truck, fiber, cable, etc.
              Otherwise the other end is always a DTE, such as another computer,
              or your serial2ethernet or serial2usb (which connects to another computer)


              hope this helps,
              =Dan
              -- 
              [ Pittsburgh 250th --- http://www2.applegate.org/~ragooman/   ]



            • Alan Outhier
              ... First, what I m about to say is not without exception. With the proper software, hardware control could be useful, but I doubt that many will come up with
              Message 6 of 9 , Jul 7, 2008
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                At 12:16 AM 7/4/2008, you wrote:
                > Don' t try to implement hardware control, it won't buy you anything.

                I think this likely good advice, but since learning is part of the
                fun, I'm trying to better understand handshaking and why it won't buy
                me anything. I'm curious about the handshaking signals provided by
                the 2SIO and the short notes in the manual about some signals.

                First, what I'm about to say is not without exception. With the proper software, hardware control could be useful, but I doubt that many will come up with such system software for an old Altair machine.

                (Receive)..Unless you're running an interrupt driven serial port, your software polls for incoming data. When the data arrives, you're either ready for it or your not. If a second character arrives before you read the first, you lose that first character. This is called an overrun. It doesn't matter how the arrival of the new data is manifested, (receive data register full, or some other status bit - set by a control line change) your software does the same thing.

                Next point - your computer will have to tell the transmit device when it's not ready or not ready to receive. Wouldn't it be a lot easier just make sure it's ready (read in the last character)?

                More could be discussed here, but time doesn't permit.

                Al
              • Tom Sanderson
                RS-232 interfacing can be simple. Three wires allow me to use an ADM- 3a to boot and run Altair BASIC. ... machine. The only time I expect to encounter a
                Message 7 of 9 , Jul 7, 2008
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                  RS-232 interfacing can be simple. Three wires allow me to use an ADM-
                  3a to boot and run Altair BASIC.

                  > First, what I'm about to say is not without exception. With the
                  > proper software, hardware control could be useful, but I doubt that
                  > many will come up with such system software for an old Altair
                  machine.

                  The only time I expect to encounter a interrupt driven serial port is
                  with MITS Timesharing BASIC.

                  An Altair can connect to Telex, Teletypes, printers, acoustic modems,
                  external modems, CRT and paper terminals, USB converters, Ethernet
                  Converters, other computers, and virtual hardware. The connection can
                  wired, wireless, cellular, or Ethernet. That collection would include
                  some non-standard devices and exceptions to general rules.

                  Software encountered by an Altair includes: MITS software, CP/M
                  software, internet protocols, Linux, Windows, Microsoft .Net, APE,
                  virtual com ports, HyperTerminal, handshaking emulation...

                  Some combinations of hardware and software will require special
                  cables and some will require handshaking or some type. Before I make
                  cables and worry about exceptions, I am questioning that capabilities
                  of the 88-2SIO and Motorola 6850.

                  To what extent can the 2SIO implement a "normal" RS-232
                  connection? "Normal" is defined by a table in the 2SIO manual. Notes
                  about DTR and RTS leave "normal" ambiguous.

                  I believe my current issues with an Ethernet converter are related to
                  disabling capabilities. My current application should work with three
                  wires. For some reason the Ethernet converter requires CTS and does
                  not like RTS from an Altair. Handshaking is disabled in the converter
                  configuration. Using LEDs to check signal status will fix the
                  symptoms. I believe a straight through connection should work. I'm in
                  the area of exceptions and special cables, but don't understand why,

                  I think we all agree that the need for Altair hardware handshaking is
                  fairly rare and prone to problems. That leads me to question the
                  proper 2SIO configuration when hardware handshaking is not used. The
                  NOTICE!! in the 2SIO manual about DCD ant CTS leave 2SIO
                  configuration ambiguous.

                  The standard MITS 2SIO cable lacks DTR and is not "normal RS-232".
                  What do we need to know for proper configuration of DTR and
                  configuratiom DCD and CTS without handshaking?

                  Tom

                  --- In altaircomputerclub@yahoogroups.com, Alan Outhier
                  <aouthier@...> wrote:
                  >
                  > At 12:16 AM 7/4/2008, you wrote:
                  > > > Don' t try to implement hardware control, it won't buy you
                  anything.
                  > >
                  > >I think this likely good advice, but since learning is part of the
                  > >fun, I'm trying to better understand handshaking and why it won't
                  buy
                  > >me anything. I'm curious about the handshaking signals provided by
                  > >the 2SIO and the short notes in the manual about some signals.
                  >
                  > First, what I'm about to say is not without exception. With the
                  > proper software, hardware control could be useful, but I doubt that
                  > many will come up with such system software for an old Altair
                  machine.
                  >
                  > (Receive)..Unless you're running an interrupt driven serial port,
                  > your software polls for incoming data. When the data arrives,
                  you're
                  > either ready for it or your not. If a second character arrives
                  before
                  > you read the first, you lose that first character. This is called
                  an
                  > overrun. It doesn't matter how the arrival of the new data is
                  > manifested, (receive data register full, or some other status bit -
                  > set by a control line change) your software does the same thing.
                  >
                  > Next point - your computer will have to tell the transmit device
                  when
                  > it's not ready or not ready to receive. Wouldn't it be a lot easier
                  > just make sure it's ready (read in the last character)?
                  >
                  > More could be discussed here, but time doesn't permit.
                  >
                  > Al
                  >
                • Craig Landrum
                  ... Over the many years of working withg RS-232 I ve found the same thing. Some UART chips handle hardware flow control nicely if programmed to do so, but some
                  Message 8 of 9 , Jul 8, 2008
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                    >>
                    >> Don' t try to implement hardware control, it won't buy you anything.
                    >>

                    Over the many years of working withg RS-232 I've found the same thing.
                    Some UART chips handle hardware flow control nicely if programmed to
                    do so, but some don't. I also tend to simply hardwire 4-5, 6-8-20 and
                    be done with it, and set up my dumb terminals for *software* flow
                    control using XON/XOFF, which most hosts recognize and most dumb
                    terminals support. It is often an option that you have to select
                    somehow on the the terminal, though.

                    FYI, XON and XOFF are ASCII control characters. XON (start sending
                    again) is cntl-Q / DC1 / 11Hex ; and the XOFF (stop sending) is
                    cntl-S / DC3 / 13Hex



                    --
                    Craig Landrum
                    Chief Technical Officer
                    mindwrap, inc.
                    Phone: (540) 675-3015 x 229
                    Fax: (540) 675-3130
                    email: craigl@...
                  • Tom Sanderson
                    ... More questions for my list: How does the Motorola 6850 fit into this picture? The 6850 and Altair 2SIO have documented support for CTS, RTS, DCD, and DTR.
                    Message 9 of 9 , Jul 8, 2008
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                      > Some UART chips handle hardware flow control nicely if programmed to
                      > do so, but some don't. ......

                      More questions for my list:

                      How does the Motorola 6850 fit into this picture? The 6850 and Altair
                      2SIO have documented support for CTS, RTS, DCD, and DTR. I'm
                      wondering what works and what doesn't?

                      To what extent will a device find the Alatair a "standard"
                      or "normal" RS232 device?

                      If I program the Altair 2SIO to handle hardware flow control nicely,
                      what problems should I expect?

                      Tom

                      --- In altaircomputerclub@yahoogroups.com, Craig Landrum <craigl@...>
                      wrote:
                      >
                      > >>
                      > >> Don' t try to implement hardware control, it won't buy you
                      anything.
                      > >>
                      >
                      > Over the many years of working withg RS-232 I've found the same
                      thing.
                      > Some UART chips handle hardware flow control nicely if programmed to
                      > do so, but some don't. I also tend to simply hardwire 4-5, 6-8-20
                      and
                      > be done with it, and set up my dumb terminals for *software* flow
                      > control using XON/XOFF, which most hosts recognize and most dumb
                      > terminals support. It is often an option that you have to select
                      > somehow on the the terminal, though.
                      >
                      > FYI, XON and XOFF are ASCII control characters. XON (start sending
                      > again) is cntl-Q / DC1 / 11Hex ; and the XOFF (stop sending) is
                      > cntl-S / DC3 / 13Hex
                      >
                      >
                      >
                      > --
                      > Craig Landrum
                      > Chief Technical Officer
                      > mindwrap, inc.
                      > Phone: (540) 675-3015 x 229
                      > Fax: (540) 675-3130
                      > email: craigl@...
                      >
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