Loading ...
Sorry, an error occurred while loading the content.
 

Re: [Altair Computer Club] Re: 88-2SIO Hardware Handshaking Issues

Expand Messages
  • 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 1 of 9 , Jul 7, 2008
      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 2 of 9 , Jul 7, 2008
        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 3 of 9 , Jul 8, 2008
          >>
          >> 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 4 of 9 , Jul 8, 2008
            > 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@...
            >
          Your message has been successfully submitted and would be delivered to recipients shortly.