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Old 20th Dec 2018, 10:13 am   #141
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 4,234
Default Re: MK14 schematic revisions

My concern other than availability would be that the BPROMs may not be fast enough when its access time is added to that of the RAM and Monitor ROM, but that would be something that would be easy enough to try out, and would make fully expanding the MK14 to 512b prom + 3k RAM possible, and would make many more complex VDU projects feasable (Like MK14 space invaders ??!!)
Don't get too ambitious, the dot resolution of the VDU in graphics mode is not terribly high. 'Pong' might be a more realistic aim.

BPROMs were used on the Nascoms, or at least one of them, as custom address decoders. They are actually surprisingly fast in terms of access speed - for that reason they were often used in things like video test pattern generators where the access speed of contemporary EPROMs might have been too slow.

However, as with all things that age they are becoming more expensive and difficult to get. GALs would be another option but only a small percentage of people have programmers capable of programming them. The parts would really need to be as ubiquitous as possible. A 'modern' fast EPROM might work just as well as an address decoder but it would come in a wide bodied footprint.
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