kit posting, what I'm working on
Brian D. Botton
botton at i88.isc.com
Fri Dec 14 18:16:07 AEST 1990
In article <1990Dec14.060413.13515 at i88.isc.com> botton at i88.isc.com (Brian D. Botton) writes:
>In article <111 at limbic.ssdl.com> gil at 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.
--
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