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 ?
CST RAM expander
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- Aurora
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- Joined: Sat Oct 25, 2014 9:53 am
Re: CST RAM expander
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.
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.
Re: CST RAM expander
Thanks Martyn - I couldn't see that for looking last night !!
A decoder would have been my guess too.
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
A decoder would have been my guess too.
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)