Thomas Your question raises some interesting points. In any asynchronous serial transfer such as RS232 the timing of an entire frame (byte) is derived from the falling edge of a start bit. You need to consider that a 10% error in clock might cause the first bit to be read 10% too soon - not a problem, however by the tenth bit a 10% error from the first bit is now an entire bit period, consider that both ends may use a clock with an error, and it's soon clear that accuracy needs to be at least 2-3% for such a transfer to be reliable with a safety margin. In your case a resonator will be fine I think. Robin Abbott - robin.abbott@dial.pipex.com ************************************************************************** * * Forest Electronic Developments * http://dspace.dial.pipex.com/robin.abbott/FED * ************************************************************************** ----- Original Message ----- From: Thomas Brandon To: Sent: 13 October 1999 00:59 Subject: Clock Accuracy > What sort of accuracy does one get with various clocks (not including RC) > for a PIC? For MIDI serial, the specs call for 1% timing accuracy. What sort > of difficulty will there be in getting a clock to this accuracy? Is there > any difference in accuracy (or other specs) between a resonator and a > crystal (or diff. types of crystal? What about higher accuracies? What is > the maximum (practical) achievable accuracy (i.e. in production, not like 1 > in a 1000 will get it) for various High speed clocks? What about driving > multiple PICs at reliable high speed, anything good for this (be nice not to > have to redesign the circuit when another PIC (and hence load > resistance\capacitance\inductance) are added? > > Thanks, > Tom.