demik
Well-known member
Just throwing out a few stupid ideas around:
If the issue is the SCC, the good thing on the Wombat board is that it's a standalone SCC and not a combo chip like in earlier Macs. On my wombat boards, the chip is Z0853008VSC which should be the 8 MHz version.
So either the chip is clocked too high and do strange things, or it just respond too late and there is collisions on the bus. Can someone measure how fast the SCC chip is clocked ? You will need either a logic analyzer or an oscilloscope.
Two things to try: clock the SCC which a different clock source, or try a faster ones. They are still produced and go up to 16 Mhz: Z0853016VSC
Faster versions do have a lower bus latency.
Datasheet is here: http://www.zilog.com/docs/serial/ps0117.pdf, pinout is page 12
The pin to check is #23 (PCLK)
If the issue is the SCC, the good thing on the Wombat board is that it's a standalone SCC and not a combo chip like in earlier Macs. On my wombat boards, the chip is Z0853008VSC which should be the 8 MHz version.
So either the chip is clocked too high and do strange things, or it just respond too late and there is collisions on the bus. Can someone measure how fast the SCC chip is clocked ? You will need either a logic analyzer or an oscilloscope.
Two things to try: clock the SCC which a different clock source, or try a faster ones. They are still produced and go up to 16 Mhz: Z0853016VSC
Faster versions do have a lower bus latency.
Datasheet is here: http://www.zilog.com/docs/serial/ps0117.pdf, pinout is page 12
The pin to check is #23 (PCLK)