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Old 16th Apr 2018, 12:07 am   #6
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 9,517
Default Re: MK14 schematic revisions

Hi Slothie - thanks for the link to the later version of the MK14 diagram, which is a new one for my collection. I didn't see your post #3 until after I had posted #4, due to your posts currently being delayed by new member moderation.

So here it is (Merry Christmas...) a scanned copy of Science Of Cambridge's official modification to early issue MK14s to remove the unwanted PROM images from the 0200-07FF address range.

I think the background to this was that I had written to them asking for details of how to expand the memory beyond its already maxed out 640 bytes, and they sent me this sheet with the handwritten comment scribbled across the top.

The first drawback (for anyone hoping to incorporate these mods into a replica) is that they are not shown in circuit diagram form, so reverse engineering the final diagram of the PCB as modified will involve looking at these physical mods and applying them to the early version MK14 circuit diagram until you have, in effect, the issue V circuit diagram.

The document does not go so far as to describe how to fit extra memory, it only describes how to free up some of the memory range so that extra RAM could be mapped into that range.

I never actually applied these mods to my own MK14: Intead, I uninstalled the VDU which was chewing up nearly all of the memory.
Attached Files
File Type: pdf MK14_EarlyIssue_AddressDecoderMods.PDF (30.7 KB, 427 views)
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