CST RAM expander

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Pr0f
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CST RAM expander

Postby Pr0f » Thu Jun 07, 2018 9:17 am

Does anyone have a circuit diagram for the CST RAM expander, or failing that if someone has one or a picture of one with which has the ROM components populated - this is the part of the board that plugs into the QL itself, - there are 4 28 pin sockets that appear to be wired up as ROM's with CS fed from a 16 pin chip of some description (it's just pads on my board)

If anyone has any info that may be helpful ?


martyn_hill
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Re: CST RAM expander

Postby martyn_hill » Thu Jun 07, 2018 10:29 am

Hi Pr0f

The QL Wiki provides an image of the CST RAM Expander, showing those 4 ROMs fitted and both a 14-pin and a 16-pin IC alongside.

The image (see here: https://qlwiki.qlforum.co.uk/lib/exe/fe ... amplus.jpg) is too blurry to make-out the full chip-markings for the 16-pin device, but it appears to be an SN74LSxxx - and, as there are not so many 16-pin ICs in the 74 series, I'm guessing its a 3-8 line decoder/multiplexer (e.g. the 74138).

EDIT: The manual also available from the QL Wiki actually includes a full chip layout diagram - very unusual! The chip in question appears to be the LS139 - "dual 2 to 4-line decoder/demultiplexer, inverting outputs"

M.


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Pr0f
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Re: CST RAM expander

Postby Pr0f » Thu Jun 07, 2018 11:31 am

Thanks Martyn - I couldn't see that for looking last night !!

A decoder would have been my guess too.

:D



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