Posted By
MMS
on 2017-03-20
13:00:28
 |  Re: Revival of interesting 'n' funny stuffs
@gerliczer: thanks for link! Today I was in a hospital, so till I wait, I had some time to read it though.
Well, then the AY 3 channel works like 3 independent 4 bit DAC, and that is pretty nice.
(if you consider, that C64 has one 4bit, and Plus/4 has one 5 bit digi channel with tricks)
So probably thta's why they have better clarity: on Plus/4 we have to force all three SID channels with mixing into one 5bit DAC, while the AY converter has three 4 bit DAC.
OFF
BTW the 8bit DAC idea on Plus/4 User port could not be easier: I just need to modify the ready C64 Digimax circuit's connection to our User port to match to the 8 bit data pins' layout, the rest is the same.
But I found that circuit a little too complex and overdone...
(it uses 4 output IC to create a stereo one, though still the mono would be a challange to get used, even without multiplexed User port data outputs  )
ZN428E latched DAC could be a little better than ZN426 resistor ladder, but I am not sure the real benefits, as on all the circuit diagrams put the Enable of the zn428 to ground, so in practice there is no difference to 426E, just more expensive.
(the MSX SCC (Konami Sound Custom Chip) was the same as ZN426E8).
Did I post the one I made 20 years ago for PC? Very small, very cute.
In case of user port even the 5V is avaiable, while on the PC Parallel port you need to get it from somewhere else, like keyboard or RS232 port (I did the later)
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