Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pasteur!agate!ucbvax!hplabs!hpda!hpcupt1!hprnd!clw
From: clw@hprnd.HP.COM (Carl Wuebker)
Newsgroups: comp.sys.ibm.pc
Subject: PS/2 COM Port Questions?
Message-ID: <1040007@hprnd.HP.COM>
Date: 5 Feb 89 17:41:14 GMT
Organization: HP Roseville Networks Division
Lines: 24


     I wrote a (stupid) terminal emulator program in Turbo Pascal 3.0.  To make
sure that I caught all the characters, I coded a Turbo Pascal ISR for the UART
receive side. It worked pretty well on the IBM-PC.  Here's what's happening
when I try to run it on a PS/2:

     * The main program uses calls 35 and 25 to save the values for the 
          existing COM port 2 ISR.
     * The interrupts are disabled briefly (CLI) then re-enabled (STI).
     * A character is written to the modem.
     * The ISR gets called, saves registers, gets the character (or characters)
          from the UART and stuffs the character in the FIFO.
     * The ISR does an EOI (Port[$20]=$20), restores registers, and IRETs.
     * The program prints a character on the screen.
     * Either the 2nd character never gets sent to the com port (com port not
          ready), the ISR never gets called for the echoed character, or the
          ISR gets called but doesn't return.

     I realize that this isn't a lot to go on; but does anyone have any clues
as to what might be causing problems on the PS/2?

Thanks,
   Carl "upgrade, (n), spend 2 months running in place" Wuebker
   clw@hprnd * HP Roseville Networks Division * (916) 785-4296