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Old 11th Jul 2018, 12:49 pm   #17
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
Default Re: Tesla MH74S571 programming.

Please find attached a .zip of the two PROM files for the MK14 'New version' OS. As they are only 512 bytes each I tried to attach them as-were but found that .bin (raw binary) is not one of the file formats allowed as an attachment. The file names include the corresponding IC numbers of the PROMs on my original issue II MK14, from which the files were read. I've never seen an issue V MK14 up close so I don't know if these IC numbers (IC2 and IC3) still hold true for that version.

It seems to be a 'widely known fact' that the MH74S571 cannot simply be programmed as though it is a Nat Semi DM74S571, but if the programming voltage really is 10.5 rather than 21V then that is one way in which it would actually be similar to, rather than different to, the DM74S571.

I did not even try to program slothie's MH devices in case I damaged them but instead passed them on to a third party who had offered to try to program them. In the event even that person had problems - one PROM programmed OK first time, but two subsequent efforts to program the second PROM led to two verification failures, at which point the remaining blank device was passed on to a third party who I think managed to program it, or another that they already had. (It ended up being quite an international effort).

My thought is that the 21V programming voltage may have been arrived at as an alternative (if so, rather risky) way to blow the fusible links in the MH device - that is, instead of making the programming pulses longer as may have been the preferred option, the solution adopted may have been to apply more voltage for the same length of time. This is purely speculation on my part, but the writer of the code obviously chose to use 10.5V originally for a reason, then apparently modified it because that seemed to be what was required to make it work.

Tesla's decision to give their device such a similar number to the DM device is puzzling and certainly misleading when traditionally all '74' series devices which have the same device number but a different manufacturer prefix are normally interchangeable, so it immediately suggests that the intention, if not the outcome, was for the MH device to be a fully compatible substitute for the DM74S571.

It would also have been in Tesla's interests for that to be the case, as there were plenty of device programmers already around which could handle the DM74S571.

Edit: One thing I can say is that the Tesla devices default to all bits=0. I specifically asked the person I sent slothie's PROMs to try reading them first before programming, to find out whether that was the case.
Attached Files
File Type: zip MK14_NewOS.zip (729 Bytes, 206 views)

Last edited by SiriusHardware; 11th Jul 2018 at 1:06 pm.
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