Date : Fri, 16 Oct 2009 13:25:36 +0100
From : bbc@... (Dave Curran)
Subject: ROM upgrades on the cheap
When I extended one of my Beebs, I followed Mark's instructions on the
page you have linked to and extended it to give me a few more. I now
have:
[MOS] [4 ROMS images] [4 ROM images] [4 ROM images] [4 banks SW RAM]
http://www.pdcurran.co.uk/BBC/DSCF2807.JPG
All four chips have links to the two address latches on IC76 and the
SW RAM links to the write latch from IC77. I used 3 x 27c512 and a
1mbit SRAM chip (only half of which is used).
The ram was a 32 pin device, so I had to make a few mods, I hard wired
the two jumper blocks (which were to allow 4K eproms?), and there is a
decoupling capacitor with its vcc lead just where pin 1 needed to go,
so I swung that around into the unused pin of the jumper block (with
was vcc), soldered one socket in there and glued in a second
freestanding socket for the other pin.
http://www.pdcurran.co.uk/BBC/DSCF2803.JPG
Not the most elegant of solutions, it would have been far neater with
just 2 SW banks, but I wanted to be able to use all 16 addresses.
Dave
2009/10/16 Rick Murray <rick@...>:
> 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...
>
>
>
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