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Old 10th Dec 2023, 6:55 pm   #120
Join Date: Jan 2021
Location: Ashford, Kent, UK
Posts: 336
Default Re: Nat Semi SC/MP Low Cost Development System

Having decided that a 100% non-functional keypad can't be made any worse, I made some repairs, hardwired the Row connections out to the edge connector and re-assembled and superglued the keypad. As a result about 50% of the keys now work. Not fantastic but it was enough to identify that the key matrix lookup table needed to shift by 1 byte in memory to produce the proper mapping. I've now been able to manually test every row/column combination and create the full key translation table including the CTRL characters. I should say that circuitboy's initial mapping of the keypad (here) based on the the MM5762 calculator chip was spot on.

Thanks to everyone that contributed their experience and time in decoding the initial EPROM dump and all the help along the way. I believe the SW is now functioning in the way that was originally intended (v11 attached). There's still some stuff left to do before putting this down, e.g. finish the schematic; source a replacement keypad; get the original MM5204 EPROM re-programmed; post something on YouTube to capture the journey. I'm probably going to make a simple 5 x 8 keypad matrix and then adjust the key mapping table to produce the correct output codes. Might also be useful if anyone wants to create a Telekit replica. It will also allow the Shift and CTRL keys to be proper keys rather than a slide switch.
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