On 2012-01-11, David J Taylor <[email protected]> wrote: > "unruh" <[email protected]> wrote in message > news:[email protected]... > [] >> Yes, I was talking about the width of the pulse's rising edge. >> It is the risetime that is of first importance for timing. The length of >> the pulse >> only is important in how the serial port identifies interrupts ( and I >> guess the possibility of the pulse been smoothed to nothing if too >> short-- but that would show up in the rise time first) > > Whether the rise-time is significant would depend on the accuracy > required. I'm assuming that the waveform is rising cleanly and without > ringing, and that the receiver circuit has hysteresis. I'm thinking > microseconds, and a 90m length of should be able to preserve risetimes of > that order. If the OP is looking for sub-microsecond accuracy, then > delays in the PPS signal may be more significant, and the delays in any > TTL-RS-232 convertor circuits etc. would start to matter.
For timing it is only the rise time that is important. The length of the pulse is irrelevant, unless your Hardware/software requires a given length pulse in order to recognize and interrupt ( and if it did , it would be broken since it had better interrupt on the rising edge if it is to be useful to timing. ) Certainly if you are using TTl-RS232 converters their times are important. However most rs232 cards will handle ttl signals fine anyway. > > Cheers, > David > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
