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Old 16th Nov 2019, 10:56 am   #18
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
Default Re: A Simple Programmer for TESLA "MH74S-" bipolar PROMs

Broadly, (I hope I am remembering this correctly) the main electrical difference between the DM and MH devices is that on the DM devices, you apply VPP (10.5V) momentarily to the data pins to be programmed, one after the other, whereas on the MH devices you connect the data pins to 0V, again one after the other, while applying VPP to another pin. So the programming regime, electrically speaking, is very different. (The MH devices also require a much longer programming pulse).

Circuitryboy pointed out earlier that the MH device programming scheme seems remarkably similar to that of the Texas SN74S.... family, although, while there are such things as SN74S287s, no one ever seems to have seen an SN74S571 so there is unfortunately no SN74S571 data sheet with which a direct comparison can be made. If you don't mind potentially wasting one more device you might like to try programming an MH74S287 as though it is an SN74S287, if your programmer supports those, rather than as a DM74S287.
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