Terminal driver for the COM port on an AT&T 6300+

[hauerwas at hvrunix.UUCP]

     The following is a message from the Vax System Manager here at
Haverford.  I'm posting it to the groups I think might know how to deal
with it.  Please respond through E-Mail to either "hauerwas!hvrunix" or
"A_HAUERWAS @ HVRFORD.BITNET"  Thanks in advance.

                               *     *     *

     I am trying to write a driver for the COM port on an AT&T 6300+ with
the OS Merge operating system.  I am able to address the chip ports and can
send single characters out on the line (a line monitor has verified this).
However, I am unable to receive interrupts.  The chip is posting the
interrupts but somehow they are getting masked out. 
	
     I am running on interrupt 4 (the default driver has been removed).  
When I read the 8259 (PIC) enable register I get a value of 13 which means
that only interrupts 0, 2, and 3 are enabled.  I enable interrupt 4 and read
the register which gives a value of 29 (as it should).  However, on the very
next instruction I read the register again and the value has returned to 13.
Any ideas?

							Bob Kostes
							Systems Manager
							Haverford College
Posted by:
-- 
Adam J. Hauerwas (Wonko the Sane)
Assistant Vax System Manager                 A_Hauerwas @ Hvrford.Bitnet
Haverford College                                  hauerwas!hvrunix
Haverford, PA  19041-1392