gc0d+@andrew.cmu.edu (Glenn Cadoret) (08/22/89)
I have been trying to write a program for an IBM-AT which will catch
interrupts from COM1. It is my understanding that three things must be done
to enable this type of interrupt:
1) Bit 7 of 0x3FB must be set low
2) Bits 0-3 of 0x3F9 must be set high
3) Bit 4 of 0x21 must be set low
I do all of these things, but I still don't see an interrupt. Specifically,
I am interested in the interrupt which is generated when a character comes
into the port.
If anyone could suggest why program is not working, it would be greatly
appreciated.
Many thanks,
Glenn
Replies to: gc0d@andrew.cmu.edu (E-mail)
(703) 760-1429 (Voice)franke@rwthinf.UUCP (Christian Franke) (09/06/89)
In article <oYwKauu00WB3IJNEhE@andrew.cmu.edu>, gc0d+@andrew.cmu.edu (Glenn Cadoret) writes: > I have been trying to write a program for an IBM-AT which will catch > interrupts from COM1. It is my understanding that three things must be done > to enable this type of interrupt: > > 1) Bit 7 of 0x3FB must be set low > 2) Bits 0-3 of 0x3F9 must be set high > 3) Bit 4 of 0x21 must be set low > > I do all of these things, but I still don't see an interrupt. [...] The OUT2 signal (Bit 3) of the Modem Control Register (0x3fc) must be set also. This is because the OUT2 signal is used to enable the hardware interrupt line of the IBM compatible serial cards. For the first tries, you should enable the receiver interrupt only, because some clone cards seem to have a problem with the generation of interrupts from multiple sources. I mentioned this problem and a workaround in a previous posting in comp.sys.ibm.pc. Regards, Christian Franke Aachen University of Technology Lehrstuhl fuer Informatik I Ahornstrasse 55 D-5100 Aachen Federal Republic of Germany Tel.: 0241 / 80-3586 UUCP: franke@rwthinf.uucp ({...mcvax}!unido!rwthinf!franke)