Xref: utzoo unix-pc.general:6858 comp.sys.att:11190
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!tellab5!laidbak!botton
From: botton@i88.isc.com (Brian D. Botton)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: kit posting, what I'm working on
Message-ID: <1990Dec14.071607.14713@i88.isc.com>
Date: 14 Dec 90 07:16:07 GMT
References: <1990Dec12.065224.10906@i88.isc.com> <111@limbic.ssdl.com> <1990Dec14.060413.13515@i88.isc.com>
Sender: usenet@i88.isc.com (Usenet News)
Organization: INTERACTIVE Systems Corporation, Naperville, IL
Lines: 27

In article <1990Dec14.060413.13515@i88.isc.com> botton@i88.isc.com (Brian D. Botton) writes:
>In article <111@limbic.ssdl.com> gil@limbic.ssdl.com (Gil Kloepfer Jr.) writes:
>>Sounds good.  There's quite a bit of software which needs to be developed
>>for the ROM though.  Only problems I see are making ROMable code from
>>the compiled (COFF) output, and maybe trying to squeeze lots into 32K.
>

  Guess what folks, I just dug out my TI memory data book and found something
very interesting.  The 3B1/7300's motherboard supports 14 address lines to the
ROMs for a max of 2 X 16k = 32k.  However, the program pin, pin 27, is not
connected, and the programming voltage pin, pin 1, is tied to +5V.  If you
look a few pages further into the data book, you come across the 27512, which
uses these 2 pins for added address lines, for a total of 2 X 64k = 128k!
  So, by running a couple of white wires we can have our cake and eat it too!
There might be a problem with pin 1, depending on where the +5V trace is, but
there are easy ways around this even if it is burried.  For those of you who
have done a P5.1 upgrade, this would be trivial.

  So, new we have the potential of 128k ROM space.  That's more then enough
for a video based ROM with built in monitor, diagnostics, alternate boot, etc.
Let me know what you think.

--
     ...     ___	     ***
   _][_n_n___i_i ________  *******		Brian D. Botton
  (____________I_I______I_I_______I		laidbak!botton  or
  /ooOOOO OOOOoo  oo oooo  oo   oo		laidbak!bilbo!brian