AST RESEARCH TECHNICAL BULLETIN TB-0032A                  4-15-85


          5251 VERSION 2.1 INTERRUPT REQUEST SELECTION


AST 5251 is configured to use IRQ 2.  If another system device is 
utilizing this interrupt,  a different interrupt request line may 
be selected.

Here is a list of valid choices and their standard uses.

               IRQ 2 = Reserved
               IRQ 3 = Asynchronous Communications (secondary)
                       SDLC Communications
                       BSC (secondary)
               IRQ 4 = Asynchronous Communications (primary)
                       BSC (primary)
               IRQ 5 = Fixed Disk (if you have the PC-XT)
               IRQ 6 = Diskette
               IRQ 7 = Printer

To select a different interrupt,  the CC432 card and the software 
must be reconfigured.

Locate the switch bank on the CC432 board.   Switches 3 through 8 
select the interrupt.

               SW 3 = IRQ 7
               SW 4 = IRQ 6
               SW 5 = IRQ 5
               SW 6 = IRQ 4
               SW 7 = IRQ 3

An ON condition selects the interrupt,  and only one IRQ position 
may be ON at any time.

To patch AST5251.EXE, it is first necessary to rename it in order 
for DEBUG.COM to edit it.   Type in the commands in boldface on a 
disk that has DOS, DEBUG and AST5251.EXE on it.

          A>REN AST5251.EXE AST5251.tst <ENTER>
          A>
          A>DEBUG AST5251.tst <ENTER>
          - e300 <ENTER>
          - 08ff:0300    0A.XX space bar 04.ZZ <ENTER>
          -W
          WRITING A000 BYTES
          -Q
          A>
          A>REN AST5251.tst AST5251.EXE
          A>

Where  XX and ZZ are equal to the value of the interrupt you have 
selected.  Use the following table for correct value:

          XX  ZZ
          0A. 04 = IRQ 2
          0B. 08 = IRQ 3
          0C. 10 = IRQ 4
          0D. 20 = IRQ 5
          0E. 40 = IRQ 6
          0F. 80 = IRQ 7