Here are pictures from superimpose unit pcb, and that side where the rgb21, minidin and balance knob are.
I double checked that irq line is not needed( did not fit it, commands work) in VHD BASIC VP commands.
Next will try to dump the vhd intermediate language program binary from Star Arthur VHD disk, as made that separate board for that part. But have to trial/error to fit proper capacitor/resistor values.
I tried to put some values based on LTSpice simulation to that VHD data circuit part, but it did not cause proper output when used in real circuit:
the original "data" signal from scope:
Anyway now i have newer PCBs that have gold plated fingers for slot connection. And option to add subboard that would contain the VHDpc data read part. Does anybody need a fully assembled cardridge pcb? Extra cables for DB25 <> DIN13 i do not have at the moment...
About the VHD data part signal reading. I connected the VHD data signal (that was connected to GND with 22K resistor) to USB sound card RCA line input and recorded the signal (at the moment just few minutes from the start until first video intro start from disk) using that USB card. I got quite low signal, but visible, that is same kind of encoded as in the VHD book. I then amplied it 20db in audacity:
But now the problem is how can i decode it from wav file, as that is now Biphase Mark Code. Manually would be pain. Also there are some mark signals there occuring once per V-synch blanking time (mark signal is the highlighted on the audicity snapshot picture), so the signal is not just pure BMC.
I know that there must be string characters also, as Star Arthur contains some text menu (for example "GAME START SELECT") before game play:
That was seen from the japan video page, that contained video from Star Arthur start:
https://sp.nicovideo.jp/watch/sm33494311?ss_id=29b4d606-5878...
by the way, i accidentally deleted my VHD folder in msx.pics, so some pics are now lost from this post topic chain.
Dawn, i made stupid error in the pcb. I put accidentally 16-pin footprint for 14-pin IC. Then autorouting made totally wrong routes because of it. So no wonder it did not work at all.
That circuit decodes the MBC bit stream individual bits based on two sequential bits ( two H-sync line frames, so 63.5us*2 ). Bit for CPU-2 changes once per 63.5us*2, but not sure is the interrupt needed at that same period. Or is interrupt triggered for total period of one bitframe (16.6927083 ms). Anyway CPU-2 gets H-sync signal for T1 input, but it also gets almoust same H-sync in VHD-7 line also for T0 input. It seems both VHD-7/VHD-9 has same periodic pattern, but some delay between these. And VHD-7 seems to be only that H-sync, but VHD-9 is H-sync with some data there during H-sync pulse
It seems i can feed LTSpice with the recorded audio track containing the VHD data bits. So from LTspice i get digital output bit stream as the 4069 based circuit works at least there:
But still then there is the part to decode those two bit pairs into one ( 01=1, 10=1, 00=0, 11=0). And then need to decode that one decoded bitstream into one VHD intermediate language 7 byte command/program data.
