Thursday, December 22, 2011
AY8930 Initial tests!
Over concerns received about the possibility that the chips were fakes I decided to test a few of them right away (Paypal customer is always right no? I might just get my money back if they are fakes)
So first thing I did was to place two of those chips on my Bagman arcade board, and the sound was just as one would expect a normal AY-3-8910 (the old version). So at least they are not broken CPUs or whatnot.
The concerns raised by my colleagues pointed towards the possibility that these were just re-branded AY-3-8910 and not AY8930's, based on the date code (2008?? if 0830 is a date code I would admit its odd for a chip designed in 1990) and on the peculiar look of the Microchip logo, also that "TAIWAN Microchip" was weird and unseen before. (though this and that beg to differ).
So I undusted my AY protoboard that I used for chipsounds research, and placed a AY8930 that was previously tested OK in Bagman. Tried a few VGMX log files, (including intv_lock_n_chase.vgmx - one of my favorite games)
First interesting discovery was that the chip didn't seem to run at 3.57MHz but at half of that (1.79MHz, just ok for the right pitch of the intv register dump). I forgot that my protoboard was last populated with a YM2149F, which uses pin 26 for clock divider (input). and my jumper was already shorted. So at least if this is a rebranded chip, its a rebranded YM2149F and not a bare AY-3-8910, since the 8910 doesn't have this feature.
Started to check out the datasheet and made a little test VGMX file that plays a simple tone and pass through
A) all 32 values of volume
B) all 8 values of Duty Cycle (PWM)
Here's a lame 'instant video' of my setup and playing both Lock 'n' Chase and then, my test file on my protoboard:
The duty cycle changes are sadly NOT seamless. This is mentioned in the datasheet as well. "The new duty cycle value will take effect immediately. This may result in one period with a "random" duty cycle at the time the register is updated."
So much for maxYMiser -alike PWM without 90% cpu usage and/or IRQ reset tricks...
I haven't yet tried the advanced LFSR noise, but I'm pretty sure this batch of chip is legit. It wouldn't make sense to copy such a chip design when theres no real demand for it. Anything is possible though....
Until next time!