From: utzoo!decvax!harpo!npoiv!npois!ucbvax!C70:info-cpm Newsgroups: fa.info-cpm Title: Re: IBM PC question Article-I.D.: ucb.1611 Posted: Mon Jul 26 23:34:34 1982 Received: Sat Jul 31 07:50:26 1982 >From COMSAT.SoftArts@Mit-Multics Mon Jul 26 23:34:23 1982 Local: William "Chops" Westfield,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