RS232 SERIAL INTERFACE: DEC LA100 PRINTER AND AT COMPATIBLE COMPUTER


          THE PROBLEM:

          Wordperfect doesn't support XON-XOFF protocol in the IBM version,
          therefore you must use hardware handshaking to prevent loss of
          characters when sending data at useful baud rates.

          THE SOLUTION:

          The LA100 provides hardware handshaking with its RESTRAINT mode
          (Busy/Ready protocol.)  This is selected by setting the
          appropriate DIP switch on the printer.  In this mode the printer
          uses pin 11 of its RS232 connector as the BUSY line: + when
          Ready, - when Busy.  This option is independent of XON-XOFF soft
          handshaking so you may leave XON-XOFF enabled which is useful if
          the printer will be shared with a DEC system such as the VT180.
          The LA100 also offers a choice of MODEM_CONTROL or
          NO_MODEM_CONTROL.  With NO_MODEM_CONTROL the LA100 ignores the
          status of its DSR, CTS, and RLSD lines.  Selecting
          NO_MODEM_CONTROL simplifies the cabling (MODEM_CONTROL is
          intended for situations when the LA100 is connected via a modem
          to a remote computer.)

          LA100               AT 9-pin       AT 25-pin

          TD   2    --->      2    RD        3    RD
          RD   3    <---      3    TD        2    TD
          GND  7    ----      5    GND       7    GND
          BUSY 11   --->      8    CTS       5    CTS
          DTR  20   --->      6    DSR       6    DSR
                              1 *  CD        8 *  CD
                              4 *  DTR       20*  DTR

          *** Some machines may need to have CD and DTR tied together.  The
          Compaq Deskpro 286 did not.

          Special thanks to Shurlo Tooker for suggesting this solution.