Thank you very much, Sean. Looking at that page, I have realized that I must have a "revision B" motherboard: it has a couple crystals (one rated at 14.24982 Mhz for general timing and other rated at 1.8432 Mhz for the serial ports), and no 74LS161 (a binary counter used as a frequency divisor in the first motherboard to obtain the clock signal needed by the 6551 serial controllers).
Looking at the schematics in my copy of the Apple //c Reference Manual, it does show the 74LS161 (which derives a slower clock signal from the master 14M signal), and marks the 1.8432 Mhz crystal as optional. And, obviously, due to the way the color carrier is generated by the Apple ][ series, the main crystal oscilator in the NTSC version (the only one covered by the Reference Manual) runs at 14.318 Mhz instead of the PAL version's 14.24982 Mhz. This frequency difference would make it impossible to derive the 1.8432 Mhz signal directly from the main 14M, making neccessary to use a second crystal and to eliminate the 74LS161. All this makes me think that, in fact, the European (PAL) version of the original //c isn't affected by the serial port bug. But then, why is my //c unable to communicate with my K7/500 at speeds higher than 300 bps? I think I will never know... And a little bit of trivia: the European //c runs at 1.023 Mhz instead of the 1.018 Mhz of the American version. This makes it 0.5% faster! Greetings, Antonio Rodr�guez (Grijan) <ftp://grijan.cjb.net:21000/> Sean Fahey ha escrito: > Here's more specific data courtesy Mitch Spector > > http://www.apple-history.com/frames/body.php?page=gallery&model=aIIc -- Apple2list is sponsored by <http://lowendmac.com/> and... / Buy books, CDs, videos, and more from Amazon.com \ / <http://www.amazon.com/exec/obidos/redirect-home/lowendmac> \ Support Low End Mac <http://lowendmac.com/lists/support.html> Apple2list info: <http://lowendmac.com/lists/apple2.html> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/apple2list%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
