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Old 16th Nov 2019, 11:44 am   #8
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: A More Useful MK14

My MK14 did have a SOC VDU connected to it for a while. (I still have it, but not connected to the MK14) As a fundamental learning aid it was useful, in the way that it demonstrated the direct relationship between bit states in memory and pixels lit / not lit on the screen (in graphics mode) or character codes in screen ram and characters on screen (in character mode). In terms of actual usefulness though, it used up so much of the 'standard' RAM that there was very little RAM left over in which to write code.

On your greatly expanded machine I would have thought it would be quite usable, since the main problem with it was insufficient RAM to support it.

The other thing I didn't like about it was the way it drastically slowed the machine down by halting it whenever it was reading data from the RAM. I had an idea at one point to put a dual-port RAM IC between the MK14 and the VDU, arranged such that the VDU could read from the dual-port RAM without having to use any of the MK14's RAM and without ever having to halt it while doing so - in the meantime the MK14 could write to or read from the RAM via the RAM's other port. I got as far as buying the dual-port RAM IC but no further than that.

My MK14 did have a small 4.00MHz crystal fitted during the 'VDU' years but as part of the recent 'restoration' drive I obtained and fitted an original 'big can' 4.33MHz crystal - apart from anything else, it makes 'Music Box' and other timing-dependent original programs run correctly again.
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