Байт (Byte): Part 6 (Trying DivMMC via Converter Board)
22I designed a converter board to plug into the 96-pin system expansion port (СИСТ) on the Байт and present a standard ZX Spectrum edge connector ... TL;DW ... it ain't working at the moment with a DivMMC (from www.thefuturewas8bit.com). I did see the ESXDOS logo briefly at one stage ...
The expansion port uses a Soviet-era СНП59-96 (SNP59) connector ... almost the same as the DIN41612 equivalent ... but using 2.5mm pitch instead of 2.54mm/0.1" pitch ... argh!
But a very kind contact in Ukraine (thanks Андрій/Andriy!!) managed to secure five of these precious connectors for me and sent them to me in Australia ... free of charge.
The Байт has two compatibility modes via the СОВМЕСТ button on the side ... one is supposed to be full Spectrum compatibility ... I've tested this earlier and it seemed legitimate.
I have also removed pins 4 & 5 of DD67 (a КР1533ИД7, an analogue of the 74LS138 3-to-8 decoder/demultiplexer) ... these pins are active-low enable pins normally tied to ground. The recommendation was to re-use these as the !ROMCS signal, tied via a 10KΩ resistor to ground. I've used Байт port A30 which connects to Spectrum edge connector A25.
So, further thinking required:
[1] Should I have added a 10µF capacitor near the edge connector as a charge reservoir for the peripheral?
[2] Is the pinout conversion correct?
[3] Is the Байт Spectrum compatibility mode not 100%?
[4] I've messed up some other way?
Further information/discussion can be found on the DIscord server.
Github repository for this board is here:
https://github.com/0ddjob/Byte_to_ZX_Spectrum