Hello all. Last weekend I wrote a short BASIC program to examine the
effects of the bits in the TEST register in Y8950 MSX-AUDIO at location
$01. Here are the preliminary results:
Y8950 MSX-AUDIO Test register $01 (write only)
Bit Description
7 Reset LFOs - seems to force the LFOs to their initial values (eg.
maximum amplitude, zero phase deviation)
6 something to do with ADPCM - bit 0 of the status register is
affected by setting this bit (PCM BSY)
5 No effect? - Waveform select enable in YM3812 OPL2 so seems
reasonable that this bit wouldn't have been used in OPL
4 No effect?
3 Faster LFOs - increases the frequencies of the LFOs and (maybe)
the timers (cf. YM2151 test register)
2 Reset phase generators - No phase generator output, but envelope
generators still work (can hear a transient when they are gated)
1 No effect?
0 Reset envelopes - Envelope generator outputs forced to maximum, so
all enabled voices sound at maximum
I will supplement this experiment with results from YM3526 OPL itself (on
a Commodore 64) and YM3812 OPL2.
Richard
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