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Old 11th Oct 2019, 6:25 pm   #12
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 4,535
Thumbs up Re: A Simple Programmer for TESLA "MH74S-" bipolar PROMs

Just thinking a bit more about this, actually - I happen to know that your MK14 is more maxed-out and has more RAM than most but the lack of a 'straight' run of 512 unused bytes of memory on the standard 'fully expanded' MK14 normally means you have to do each PROM 256 nibbles at a time, so it takes a total of four runs to program a set of two PROMs.

For code which is likely to be programmed into PROMs more than once it might be useful to pre-pack the 512 nibbles of the code to be programmed into the 256 bytes of 'extra RAM', various schemes are possible but you could for example pack them like this:

Ram byte         Contains 
0                nibble 0 and nibble 1
1                nibble 2 and nibble 3
2                nibble 4 and nibble 5
3                nibble 6 and nibble 7
...and so on, all the way up to RAM byte 255 / nibble 511. Nowadays we can just write a bit of code on something else to trawl all 512 nibbles from an 8-bit wide hex file and write them out to a 'packed' file ready to be loaded into the 256-byte extra RAM, a luxury we didn't have back in the day when the MK14 was the only 'computer' we had.

It would need a slightly adapted version of the PROM blower code, but pre-packing the code to be blown in this way would allow the 512 locations of each PROM to be blown in one run, halving the chance of mucking something up / loading the wrong section of code / programming the lower half of the PROM twice, etc.

If it is a copy of the MK14's OS that is to be blown into the PROMs then the 'standard' version of the PROM blower code could be altered to read all 512 low nibbles of the OS or all 512 high nibbles of the OS and program them into a PROM in a single run.
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