[fa.info-cpm] IBM PC question

C70:info-cpm (07/24/82)

>From BILLW@Sri-Kl Fri Jul 23 21:16:00 1982
Has anybody gotten the IBM PC serial IO card to work using interupts ?
I no this is possible because IBM sells software that does it (without
sources. grr). However, I seem to run into a problem that the interupt
service routine never gets called, that is, not until I run another
program, at which point it starts executing grabage (this is because
I never turn things off, but as far as I can tell, they never get turned
on either.)  Im baffled.  Help.  You can look at what im trying to do
in SRI-KL:<BILLW>IBMPC.A86....

Thanks
Bill W

C70:info-cpm (07/27/82)

>From COMSAT.SoftArts@Mit-Multics Mon Jul 26 23:34:23 1982
Local:  William "Chops" Westfield <BillW@Sri-Kl>,info-cpm at BRL
Original-date:  26 JUL 1982 08:33:28
Via:  Mit-Multics; 26 Jul 82 23:05-EDT
Via:  Brl; 26 Jul 82 23:15-EDT
Via:  Brl-Bmd; 26 Jul 82 23:32-EDT

IBM failed to fully document everything that you need in order
to get the RS232 to interrupt.  The "user-defined" pin OUT2 on
the communications chip MUST be asserted if you wish to ever see
an interrupt.  If you do the following, your program will work
correctly:

1. Set DLAB = 1 via LCR port
2. Output the baud rate divisor
3. Output the line control bits via LCR port
4. Set the modem control register (use the following as a guide)

     mov       al,$0b                    ; DTR, RTS, OUT2 (UNDOCUMENTED)
     mov       dx,rs232_mcr_port         ; modem control
     out       al,dx

5. Set the interrupt mode via IER port
6. Enable the i8259a interrupt for the rs232

Hope this helps...
-- Ray