TI-H: TI-92 Link Port

To: ti-hardware@lists.ticalc.org
Subject: TI-H: TI-92 Link Port
From: Bryan Rittmeyer <bryanr@flash.net>
Date: Tue, 19 Aug 1997 14:04:45 -0400
Reply-To: ti-hardware@lists.ticalc.org

Hi,

As most of you know, Bryan Turner figured out how to do "direct" I/O
with the TI-92 link port (I.E. read/control the link port lines
individually.) I wrote a small program called "port" which is posted
on the Extender web site... however, as I was working on the
Extender uP today I found a few interesting things.

a) If you read the link port bits (via direct input) within a small
amount of time after writing to them, the calculator will lock up.
This makes it VERY hard to use a fast custom protocol on the TI-92.
(I am not sure if the calculator locks, or if direct access simply
fails -- I am almost sure it is the later, though)

b) If you send a large amount of data, via the TI protocol, to the
TI-92 and read it in via the ROM routines, after about 130 bytes
the routines will simply fail, and no more data will be input until
the link port is reset. If you slow down the sending, by about
50 uS/byte, the routines work fine, all of the time. This is why
I need a 260+ cycle loop between each BYTE within the EuP firmware.
Needless to say that doesn't help the data rate any.

I am wondering if anyone out there has ideas on what is causing either
of these two things... I have a feeling they are results of the same
problem.

I'm going to be decompiling the ROM send/receive routines today to
see what I can ascertain.

Bryan Rittmeyer
bryanr@flash.net