Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!philabs!cmcl2!floyd!vax135!ariel!hou5f!orion!houca!hogpc!houxm!ihnp4!ixn5c!inuxc!pur-ee!CSvax:Pucc-H:ac4
From: CSvax:Pucc-H:ac4@pur-ee.UUCP
Newsgroups: net.micro.pc
Subject: Re: wizards needed - RS232 card and interrupts
Message-ID: <135@pucc-h.UUCP>
Date: Wed, 22-Jun-83 22:41:07 EDT
Article-I.D.: pucc-h.135
Posted: Wed Jun 22 22:41:07 1983
Date-Received: Fri, 24-Jun-83 12:01:05 EDT
References: cvl.413
Lines: 20


   The folks at IBM have hidden some cute tricks up their sleeves 
to handle their communications interrupts.  Check the technical
reference manual page D-48 (logic diagram) and you will note that
they have used the auxilliary output "OUT2" from the modem control
register to mask off the INTRPT line.  If you don't set OUT2, you
will get nothing!  No mention of this appears in the section on
programming the INS-8250 - just a regurgitation of the chip specs.

   You do need to worry about the 8259 interrupt controller.
The asynch comm adaptor uses interrupt level 4.  You must set
the interrupt mask register to enable level 4 (set the bit=0).
You must also acknowledge each interrupt in the interrupt request
register using the "end-if-interrupt" signal for level 4.

   Good luck!
	Tom Putnam
	Purdue University Computing Center
	...decvax!pur-ee!pucc-h:ac4
	(317)494-1787