Hello!
I hope someone can help me I have a 25 y/o MIDI keyboard back out of storage during Scotland's national lockdown. The serial MIDI data seems to be running slow (more like 28.9kbaud rather than the 31.25+-1% standard) which is causing misclocking of the data in to registers of the PC's adapter and garbled messages. Inside the keyboard I found a simple PCB with what appears to be two microcontrollers, U1 sampling the keys & U2 the handling the MIDI data. U2 is not identifiable but I guess is a 28pin Zilog Z8 series, likewise the Y1 2pin timing device connected with two caps to the XTAL pins of U2.
Y1 and its markings "2S0800A" suggest this may be a ceramic resonator rather than a crystal, which might also explain the significant drift with time. I didn't expect to see much on its pins (U2 9&10) even with a x10 probe but there is a perfect sinewave between one pin and gnd at 0.71kHz 400mVp-p. There is a constant square wave on pin 7 at 42kHz duty cycle about 20% connected to U1 presumably synchronising the two with a multiplier of 60, odd multiple.
Could anyone shed light on the resonator running this microcontroller, does 800 mean 800hz, now drifted to 710 (about the 10% error in the baud rate)? Isn't this very low? Is there a better way to measure its frequency without removing from the board?
Olly

 

What you have is probably a crystal. Ceramic resonators usually have the capacitors built in.

 

hi,
The only bit of info I can find is this,, not convincing.?
E

 

Thanks Keith, I was surprised a crystal would drift 10% while in storage?
Looks like a Google OCR error unfortunately Eric, when I look at the PDF its unrelated and 2SD800, thanks though.
Olly