Apple II hardware design

"A.R. Duell" <ard12(a)eng.cam.ac.uk> writes: Hmm? What was that bit-banged serial port? If you look in the Apple ][ red book, there is a little circuit in there that plugs into the game I/O connector and drives a 20mA current loop. Alongside there is a short assembly program to drive it. Now there is a bit-banger. There was an unspectacular serial card for the ][. I don't recall it being a bit banger, just that the combination of it and the printer I was using at the time (an IDS BrighterWriter) wasn't smart enough to manage any sort of common flow control, so that I had to run it at 300 baud. I thought it had some sort of UART-like thing, but maybe my brain is going again. Hmm, I think it was called the Asynchronous Serial Interface or something like that. There was also a Synchronous Serial Interface that (I recently found out) was the Silentype printer interface. I don't remember the Mountain Hardware CPS card that well, and I feel very good about that based on what I do remember. Now there was a klu[d]ge. The Apple Super Serial Card was designed around a 6551. There were a couple of other cards designed around the 6850. The Hayes Micromodem ][ was one of these. ... Strange as it seems today (now that I have done some programming around PC-contemptible serial ports), the Apple ][ serial cards and software generally worked by software-polling-hardware. The only serial card I can remember supporting interrupts was the Super Serial Card, and I can't say that I ever saw it used that way. Certainly none of the "standard" software required it; interrupts just weren't generally done on Apple ][s. -Frank McConnell