| ??? 02/15/06 17:40 Read: times |
#110084 - forget mode 0, im that mode there is no Responding to: ???'s previous message |
... 12 MHz .... It's not just convenient in the case of the mode 0 serial port, but it's essential.
Forget mode 0, in that mode there is no reason to use a "baud rate crystal". I am starting another thread "who is using mode 0" and doubt the "yes"es will be many It's not about the arithmetic. It's about making all the pieces fit. It's about being able to use the correct frequency rather than being contained by an old habit. I've been puzzled for years about why this is such a "religious" issue. Not the correct frequency, that is irrelevant, but the correct baud rate. Using http://www.keil.com/c51/baudrate.asp you find that at 12MHz with timer 1, 4800 baud is the best you can get, for 9600 you get a 7.5% error which is not acceptable. Using T2, the best you can get with 12MHz is 28.8k. Again many derivatives do not have T2 and some apps require T2s capabilities for other things so here is the answer to the original question "does anybody use those "low" baud rates?" YES, those that use a "processor crystal" rather than an UART crystal" The classic parts have only one serial port and two timers. As it happens, the newer Maxim/Dallas parts have two serial ports and, I believe three timers. That adds another level of complexity to the question of how to pick the system clock rate. au contraire, it makes it much simple, see above. but I've yet to see a compelling argument for the old slightly more than 11MHz. well, here it is Most folks don't use the UART at all HUH? I would say that, at least. 90% of '51 apps have a serial connection to something else. Erik |
