Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!seas.gwu.edu!viraf
From: viraf@seas.gwu.edu (Viraf Bankwalla)
Newsgroups: comp.os.msdos.programmer
Subject: U8250 Questions
Message-ID: <2535@sparko.gwu.edu>
Date: 14 Jan 91 23:52:19 GMT
Reply-To: viraf@seas.gwu.edu ()
Organization: The George Washington University, Washington D.C.
Lines: 34

Hi,

  I'm writing an isr to handle COM1 and COM2, and had a couple 
  of questions.

  The Interrupt Identification Register indicates if an 
  interrupt is pending, and which one it is.  The interrupts
  are assigned priorities, the higest one being serviced first.

	   PRIORITY        Interrupt ID
	   --------        -------------------------------
		  1            Receive Line Status
		  2            Receive Data Available
		  3            Transmit Holding Register Empty
		  4            Modem Status Changed

  Say I'm in my isr, processing Receive Data Available,
  and the modem status changes, am I interrupted, or
  will I notice the change the next time I poll the
  IIR in the loop, as I havn't issued the End Of Interrupt ?

  I've also noticed, that on turning the modem OFF, the DCD,
  and other bits in the Modem Status Register get set, resulting
  in me returning a false result.
  Assuming that DCD always reflects the true state of the
  carrier, how could I avoid the above problem ?

  Any help, and references would be greatly appreciated.

  Thanks in advance.

  viraf bankwalla
  viraf@seas.gwu.edu
  ...!uunet!gwusun!viraf