Date   : Fri, 16 Oct 2009 00:16:33 +0100
From   : jumbos.bazzar@... (Mark Haysman)
Subject: ROM upgrades on the cheap

Hi.

You just connect pin 27 of IC101 to pin 27 of IC100 instead of the R/W 
signal. You still need to make the cut to isolate it of course.

Mark.

> 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