jdm@gssc.UUCP (02/02/87)
i am considering buying an atari, but my application demands rs-422. after looking at the sams schematics and the abacus books, i have discovered that if you put a switch on the 2.4567 MHz crystal on the mc68901 such that at the flip of a switch you drive the XTAL inputs with 4Mhz (which happens to be the clock input of the chip) you can then drive the 68901 at its maximum rated speed. what this means is that if you go stomp on the timer D registers such that you are in synchronous mode, you can do rs-422 synchronouse at 500K baud (4 Mbits/second). you also need to set the timer C prescalers to cause it to tick at 200msec, as some apps use this as "system time". i don't have the books with me, or i'd give more details, but if someone would like to try this, i know *i'd* be interested. please e-mail me for more details on what i was thinking. the real question is, why didn't atari have the forsight to use this higher clock rate for the 68901, and why didn't they provide rs-422 driver software? seems like the obvious thing to do, if you are to compete with le Mac. thanks, -- jdm