Thread View: comp.sys.ibm.pc.programmer
2 messages
2 total messages
Started by Bryan So
Sat, 16 Jun 1990 00:20
Accessing COM3 and COM4
Author: Bryan So
Date: Sat, 16 Jun 1990 00:20
Date: Sat, 16 Jun 1990 00:20
11 lines
710 bytes
710 bytes
Somebody must have posted this before, but I am relatively new to this newsgroup, so... can somebody show me the general method to speak to COM3 and COM4? Can I simply service IRQ3 & IRQ4 as if they are COM1 and COM2? If so, how can I distinguish whether the interrupt is raised by COM1 or COM3 (take IRQ3 for example)? Thanks in advance. Bryan So
Re: Accessing COM3 and COM4
Author: david nugent
Date: Mon, 18 Jun 1990 05:30
Date: Mon, 18 Jun 1990 05:30
29 lines
1471 bytes
1471 bytes
In <10595@spool.cs.wisc.edu> so@brownie.cs.wisc.edu (Bryan So) writes:
>Somebody must have posted this before, but I am relatively new to
>this newsgroup, so... can somebody show me the general method to
>speak to COM3 and COM4? Can I simply service IRQ3 & IRQ4 as if
>they are COM1 and COM2?
In general, yes.
>If so, how can I distinguish whether the
>interrupt is raised by COM1 or COM3 (take IRQ3 for example)?
Test each UART's EID register. Bit 0 will be low if there's an
interrupt active. The rest of the bits in this register identify
the interrupt type(s).
Most cards with 4 ports don't support sharing of interrupts between
ports correctly (unless they explicitly state that they do), but if
they do you can look at both to determine which it was. Depending
on the speed of the links, you may have to service received characters
on both ports before moving on and servicing other less urgent
things.
david
--
* Unique Computing Pty Ltd, Melbourne, Australia. *
david@csource.oz.au 3:632/348@fidonet 28:4100/1@signet
Thread Navigation
This is a paginated view of messages in the thread with full content displayed inline.
Messages are displayed in chronological order, with the original post highlighted in green.
Use pagination controls to navigate through all messages in large threads.
Back to All Threads