any way to set AY PSG phase?

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Enlighted (5618)

ARTRAG's picture

11-01-2017, 20:28

Grauw wrote:

I tested PSG period=0 with my oscilloscope, post from a year or maybe two ago should be here somewhere on the forum; iirc period=0 is identical to period=1 (rapid oscillation).

This is interesting, what was you probing with the oscilloscope?
Directly the ay8910 pins or the audio port ? I would surprised to see a signal at 110kHz not filtered by the audio circuitry.

By Grauw

Enlighted (5405)

Grauw's picture

11-01-2017, 22:26

Some #openmsx chatlog from december 2014 I found:


22:37 grauw: hmm, maybe it’s me, but shouldn’t setting a period of 0 disable the AY3 oscillator and always generate a high output?
22:39 grauw: looking at the PSG recorded output from openMSX, as well as the source code ("Also, note that period = 0 is the same as period = 1."), it still oscillates
22:49 Quibus: "Also, note that period = 0 is the same as period = 1." This is mentioned in the YM2203 data sheets.
22:50 grauw: MSX has AY3 or YM2149 so I don’t know how useful that info is
22:50 Quibus: that's n OPN, so I wonder why it's mentioned
22:51 Quibus: compatibel met software voor de Yamaha YM2149 en General Instrument AY-3-8910/12
22:51 Quibus: it has it included it seems
22:51 grauw: yes
22:51 grauw: but this kind of edge case behaviour, I don’t know if you can assume that is identical
22:53 Quibus: that comment was written in 2004
22:53 Quibus: Try it on your real hw :-)
22:53 grauw: note that the ear may not be able to distinguish between a signal oscillating at 224 khz and one continuously high, so...
22:53 grauw: I was thinking of doing that, but I wonder if I can see that when recording from a 48kHz
22:54 Quibus: comment comes directly from MAME:
23:05 grauw: my sound card doesn’t pick up any difference between period = 0 and period = 4, only at period = 5 (44.7 kHz) it starts to register
23:06 grauw: or maybe that’s 89.5 kHz
23:06 grauw: anyway that doesn’t help :)
18:35 grauw: I checked the PSG output for period 0 with my new oscilloscope
18:35 grauw: it is indeed identical to period 1 so the openMSX implementation is correct
18:40 grauw: the OPN’s PSG’s behaviour is officially documented, if that’s what you mean
18:41 grauw: when I brought it up the other day nobody told me it was confirmed for the AY3
18:41 grauw: though, actually, I tried on the CX5MII so that’d be the YM2149
18:54 grauw: anyway, stupid HB-75P doesn’t have a separate audio out :(
18:54 grauw: hmm what would be the best way to get the audio to my amplifier without cutting cables...
18:55 hap: open up and probe the pins :|
18:55 grauw: mhhrmrm so much trouble I don’t wanna
19:18 grauw: ok I just checked my HB-75P, it generates the same waveform for period 0 and 1 too
19:18 grauw: poked the probes into the scart connector ;p

I’m assuming I for myself sufficiently confirmed that it was indeed still the PSG signal, by seeing the wave length differences when stepping to lower periods, but it’s been a while ago.


Enlighted (5618)

ARTRAG's picture

12-01-2017, 08:04

In this case you should add a note in the psg page on your site

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