On Fri, 2 Sep 2011 21:26:10 +0200 Uwe Bonnes <[email protected]> wrote:
> >>>>> "Jim" == Jim Paris <[email protected]> writes: > > ... > >> results. However with the RS232 pattern you can't easily measure > >> exact frequency with the scope. > ^^^^^ > Jim> If you send a continuous string of UUUUU then you'll see the base > Jim> frequency as a simple square wave. > > But the square wave is disturbed by the start/stop bits and the > turnaround between bytes. So you can estimate the frequency, but not measure > exact. > Well, yes, but... every UART I've ever tested will send the start bit of an already-queued byte immediately at the end of the requested number of stop bits. The ASCII value for 'U' is 0x55, so its bit pattern is <start0>10101010<stop1>. If you set up no parity, 8 bit, one stop and send UUUUUUUUU then this really does produce a perfect square-wave. Of course, the scope will report the frequency in terms of full cycles, so that's half the Baud rate. Cheers, Rob -- libftdi - see http://www.intra2net.com/en/developer/libftdi for details. To unsubscribe send a mail to [email protected]
