RS-232 Interface Board  (250-1031)    Settings         Faxback Doc. # 5571


PLUS RS-232 Interface Board (250-1031)* DB-25 female connector

There are hardware modification for this board.  Check with your Radio 
Shack Service Center to make sure these modifications have been applied to 
your board. If used with 1000HX or 1000EX no additional boards are 
required.  Requires 250-1016 Adapter Board if not used on a Memory PLUS
Expansion Board.  This RS-232 Board is an Asynchronous port that supports
from 50 BAUD to 9600 BAUD. It also supports 5-, 6-, 7-, or 8-bit characters
with 1, 1-1/2, or 2 stop bits.

───────┬───────────┬─────────────┬──────────────────┬─────────────────────┐
Port   │    COM1   │     COM2    │        COM3      │       COM4          │
───────┼───────────┼─────────────┼──────────────────┼─────────────────────┤
Add    │  3F8-3FF  │      2F8-2FF│        3E8-3EF   │       2E8-2EF       │
───────┼───────────┼───────────┬─┴─────────┬────────┴──┬────────┬─────────┤
Int    │    IRQ4   │     IRQ3  │    IRQ4   │      IRQ2 │  IRQ3  │  IRQ5   │
───────┼───────────┼───────────┼───────────┼───────────┼────────┼─────────┤
DIP    │  1 2 3 4  │  1 2 3 4  │  1 2 3 4  │  1 2 3 4  │ 1 2 3 4│  1 2 3 4│
Sw  ON │        X  │    X   X  │  X     X  │  X   X X  │ X X   X│  X X X X│
───────┼───────────┼───────────┼───────────┼───────────┼────────┼─────────┤
Sw  OFF│  X X X    │  X   X    │    X X    │    X      │      X │         │
───────┴───────────┴───────────┴───────────┴───────────┴────────┴─────────
Note: 1. Setting all switches to OFF position disables the board.
      2. On Tandy 3000-series computers, do not set the switches to use
         IRQ2 for interrupt signals.
      3. On Tandy 1000-series computers, do not set the switches to use
         IRQ5 for interrupt signals.

I/O PORT SELECTION

DIP switches let you assign the I/O address spaces for each board in case 
you use several serial devices at the same time. At the factory, the 
switches are set at COM1, which takes the I/O address spaces of 3F8-3FF.

 PORT             COM1              COM2
ADDRESS          3F8-3FF           2F8-2FF
                  IRQ4              IRQ3
            ┌───────────────┐ ┌───────────────┐
            │ 1   2   3   4 │ │ 1   2   3   4 │
            │┌─┐ ┌─┐ ┌─┐ ┌┬┐│ │┌─┐ ┌┬┐ ┌─┐ ┌┬┐│
            │├┬┤ ├┬┤ ├┬┤ ├┴┤│ │├┬┤ ├┴┤ ├┬┤ ├┴┤│
            │└┴┘ └┴┘ └┴┘ └─┘│ │└┴┘ └─┘ └┴┘ └─┘│
            └───────────────┘ └───────────────┘
                           COM3
                          3E8-3EF
                  IRQ4              IRQ2
            ┌───────────────┐ ┌───────────────┐
            │ 1   2   3   4 │ │ 1   2   3   4 │
            │┌┬┐ ┌─┐ ┌─┐ ┌┬┐│ │┌┬┐ ┌─┐ ┌┬┐ ┌┬┐│
            │├┴┤ ├┬┤ ├┬┤ ├┴┤│ │├┴┤ ├┬┤ ├┴┤ ├┴┤│
            │└─┘ └┴┘ └┴┘ └─┘│ │└─┘ └┴┘ └─┘ └─┘│
            └───────────────┘ └───────────────┘

                           COM4
                          2E8-2EF
                  IRQ3              IRQ5
            ┌───────────────┐ ┌───────────────┐
            │ 1   2   3   4 │ │ 1   2   3   4 │
            │┌┬┐ ┌┬┐ ┌─┐ ┌┬┐│ │┌┬┐ ┌┬┐ ┌┬┐ ┌┬┐│
            │├┴┤ ├┴┤ ├┬┤ ├┴┤│ │├┴┤ ├┴┤ ├┴┤ ├┴┤│
            │└─┘ └─┘ └┴┘ └─┘│ │└─┘ └─┘ └─┘ └─┘│
            └───────────────┘ └───────────────┘

If you plan to use only one serial device, you do not have to change the
setting. However, if you have already installed a serial printer or another
serial device etc., change the position of the switches to set the board to
COM2 (or COM3/COM4 accordingly, in the case of several devices in use).

Depending on the switch setting, one of the interrupt signals IRQ2-IRQ5 is
output to your computer to inform it of the I/O unit's condition. Because 
COM3 and COM4 can be set in two ways--each having different interrupt
signals--select either setting, referring to your computer owner's manual.

NOTES: 1. Setting all switches to OFF position disables any interrupt 
          signal.
       2. On Tandy 3000 series computers, do not set the switches to use 
          IRQ2 for interrupt signals. When you have to set the board to 
          COM3, set it for IRQ4, or disable the interrupt signal by setting
          all the switches to OFF position.
       3. On Tandy 1000 series computers, do not set the switches to use 
          IRQ5 for interrupt signals. When you have to set the board to 
          COM4, set it for IRQ3, or disable the interrupt signal by setting
          all the switches to OFF position.


(smm/tmc-06/27/95)