Date   : Thu, 22 Dec 1983 12:07:37 EST
From   : Keith Petersen <w8sdz@brl>
Subject: USR S-100 modem overlay for MDM7xx

Phil Lapsley has released a new overlay for MDM7xx for the new US
Robotics 300/1200 baud S-100 modem.  The overlay works on MDM712 and
later (including the latest MDM715).  It's available on SIMTEL20 in the
MICRO:<CPM.MODEM7> directory as M7US-1.ASM.

Dave Hardy (Microsystems author and Sysop of TCBBS Dearborn MI) had one
of these modems for evaluation several months ago.  He ran into some
problems trying to use it with the BYE program on his Sysop
Clearinghouse RCPM but eventually found what was wrong.  I suggested
that Phil contact Dave for details and here's some information that Dave
Hardy passed along which may belp others trying to use this modem with
BYE.

----- Forwarded message # 1:

Date: Wed, 21 Dec 83 11:14:48 pst
From: The tty of Phil Lapsley <jlapsley%D.CC@Berkeley>
To: w8sdz@brl
Subject: USR overlay

   I talked with Dave Hardy this morning, and we hashed out a few
things. His problem was on auto-answer, which mdm715 doesn't really have
to cope with.  On AA, the USR changes the baud rate to suit the incoming
call, but it never tells anyone that it changed.  Therefore, things get
excellent when one tries to send commands to it when it is at a
different baud rate than one expected.

   But he confirmed what I suspected: the board is not meant to run
faster than 4 MHz (i.e., my 5) and he agreed I should have some
time-padding do nothing stuff in there to slow things down (as an aside,
another flaw on the board is there is no provision for wait states).

   In M7US-1.ASM the initialization routine are two XCHG statements
after each OUT statement. They are commented-out (i.e., ";        XCHG")
so they will not be there for people who use slower systems.  However,
there is a note explain- ing what they are for and telling people with
fast systems to remove the semi- colons and fix things up.

   I have tested this one fairly extensively, and without the delay it
locks up.  With the delay I have yet to be able to cause it to lock. 

---Phil

----- End of forwarded messages