Author: Lyndon Amsdon (webport-cl6-cache2.ilford.mdip.bt.net)
Date: 12-10-2002 22:55
The ACIAs require two clocks, one the baud rate clock (derived from the bus frequency) and the other the system clock that all data is synced with. The ACIA is a syncrounous device.
Falcon bus speeders mess up the baud rate, thus keyboard/midi go at the wrong speed and a 500Khz is needed to get the right baud rate again, pins 3+4 IIRC.
When you speed the ST CPU the E clock is increased and this is why these don't work without extra circuitry. The E clock is one tenth of the CPU speed, ie 800KHz, but with 60/40 duty cycle.
68020 and up don't have interface for "old" 6800 synchrounous stuff so the GALs in the Falcon handle the communication between the two.
I'm sure 68010 lacks something, maybe the 6800 interface or less IRQ levels. Maybe I'm thinking of the 48pin 68000.
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