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From: hennesse@dtrc.dt.navy.mil (Hennessey)
Newsgroups: comp.sys.ibm.pc
Subject: AT Interrupt Controller Programming Question
Message-ID: <695@nems.dt.navy.mil>
Date: 27 Dec 89 13:56:40 GMT
Sender: news@nems.dt.navy.mil
Reply-To: hennesse@dtrc.dt.navy.mil (David Hennessey)
Organization: David Taylor Research Center, Bethesda, MD
Lines: 20

I have a interrupt-driven serial port driver that works fine on the PC, but
does not work on an AT. It seems that some interrupt occurs, and the controller
is not reset, causing a lack of interrupts.

If I remember correctly, the AT computer uses 2 8259A interrupt controllers.,
instead of one like the PC.

I need programming details: 

  Where is the second chip (I/O addresses A0 and A1???)

  What does the second chip service?

  How do you set the interrupt mask register (I/O port 21 on the PC)

  How do you reset after servicing the interrupt?

Thanks...

Dave (301) 227-1400