Adding more RAM to the TI85 internally using SRAMS and port 5 for

Adding more RAM to the TI85 internally using SRAMS and port 5 for chip select

To: CALC-TI@LISTS.PPP.TI.COM
Subject: Adding more RAM to the TI85 internally using SRAMS and port 5 for chip select
From: David Teitlebaum <david.t@SYLVANIA.SEV.ORG>
Date: Fri, 6 Jun 1997 03:23:07 GMT
Organization: a Digital Internet AlphaServer Site
Reply-To: David Teitlebaum <david.t@SYLVANIA.SEV.ORG>
Xref: paladin.american.edu bit.listserv.calc-ti:14034

        I was wondering if anyone with any electrical knowledge knew
if more ram could be added to the TI85 by using port 5 to change the
memory page to something above 7 and have a demultiplexer chip
interpret this and activate an additional ram chip which would use the
same data lines as the rom chip to give more memory, easily accessed
through zshell and much faster/less expensive/less processor intensive
than the "expander" which uses a slow, less reliable eeprom to store
data.  This would not affect normal funcioning of the calculator since
the rom is never going to change the page to anything other than 0-7
so it seems like it could work.  All you would have to do is change
the value of port 5 in a zshell program and then access those
addresses which used to be rom.  Then set it back before leaving (of
course).  I think my understanding of this is correct but I might be
wrong, so someone who knows for sure please say so.  Anyone with
intelligent suggestions care to commment?
David Teitlebaum
david.t@sylvania.sev.org