Date   : Fri, 16 Oct 2009 01:11:24 +0200
From   : rick@... (Rick Murray)
Subject: ROM upgrades on the cheap

Hello,

I am hoping somebody has already done this, so I can pick your brains 
instead of poring over the circuit diagram armed with datasheets...

With reference to:
   http://www.retroclinic.com/acorn/swr/swr.htm

I am not that interested in SRAM, but the ability to have IC100 and 
IC101 take up to four ROM images in a larger EPROM.
Obviously pin 27 of IC101 will need to be altered as the RAM write 
strobe is not relevant. Pin 27 should go to the ROM select latch, yes? 
But where? That's the question!



The hoped-for eventual idea is:

  .------.  .------.  .------.  .------.  .------.
  |      |  |      |  |      |  |      |  |      |
  |      |  |      |  |      |  |4 ROM |  |4 ROM |
  | MOS  |  |BASIC |  | DNFS |  |IMAGES|  |IMAGES|
  |      |  |      |  |      |  | HERE |  | HERE |
  |      |  |      |  |      |  |      |  |      |
  '------'  '------'  '------'  '------'  '------'
   IC51      IC52      IC88      IC100     IC101



Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...