Date   : Thu, 17 May 1984 13:38:00 PDT
From   : SSalzman.ES@XEROX.ARPA
Subject: Getting MEX running...

Hello. Before knocking the program, which in my opinion is a very fine piece of
work, the MEXNEWS.001 said that there's an error in the documentation regar-
ding the fact that MEX should come up the first time around. It won't. Your
hardware overlay must be installed first. After reading that you have an
MD-2 I realized that you have an additional problem. This is due to the
carelessness of whomever wrote the M7MD-1 overlay for MDM7xx. There
is a bunch of stuff missing that MEX looks for that I suppose MDM7xx can do
with out. I have a Xerox 820-II and my overlay has all the proper settings to
work with MEX. A good friend of mine has an MD-3 (same overlay as the
MD-2) and I helped him install it. Now for the details. 

The first thing to do is to add the following equates to your overaly (same
area as your ports are defined):

MODRCVB:	EQU	2
MODRCVR:	EQU	2
MODSNDB:	EQU	1
MODSNDR:	EQU	1

Next, locate the following :

IN$MODDATP	IN	MODDATP ! RET	;Comments...
			DS	31

And replace the 'DS 31' with the following chunk of code:

			DS	7			;
ANI$MODRCVB	ANI	MODRCVB ! RET	;bit to test for recv	148h
CPI$MODRCVR	CPI	MODRCVR ! RET	;value when ready	14bh
ANI$MODSNDB	ANI	MODSNDB ! RET	;bit to test for send	14eh
CPI$MODSNDR	CPI	MODSNDR ! RET	;value when ready	151h
			DS	6						154h
OUT$MODCTL1	OUT	MODCTL1 ! RET	;out modem ctl port	15ah
OUT$MODCTL2	OUT	MODCTL2 ! RET	;out modem status port 15dh

Note the hex numbers to the right, Those are the addresses of the code added 
that takes place of the DS 31. Look at the .PRN file and make sure the
addresses
match. I'm doing this pretty much from memory (though I'm pretty sure it's
correct). If you have problems, let me know and I'll check into it.

Overall, if you have an overaly that doesn't work, It's probably because
there is some important info missing, not because of MEX.

				- Isaac Salzman

Ssalzman.es@Xerox