David Woolley <da...@ex.djwhome.demon.co.uk.invalid> writes: >Unruh wrote:
>> Garmin defines the leading edge as the transition from 0V to 5V on the PPS >> line. Now serial has two levels -12V and +12V. with capacitive coupling, That was supposed to be a capital W and the beginning of a new sentence. Sorry. >There's no capacitive coupling; it is assumed that the transmission line > and load behave as capacitive, but that is in parallel. >The transition region for RS232C is -3V to +3V into 4 to 5k. Yes, and 0 V lies right in the middle of that, and teh behaviour is apt to be undefined. >> the garmin signal would be something like -2.5V to 2.5 V which really is >However, the expected hysterisis is in the 10s to 100s of mV range, and >the actual threshold for control signals is supposed to be above zero, >such that zero volts will give an unambiguous off state. >In practice, therefore, with real world RS 232 line receivers, there is >no problem in feeding from TTL levels, as long as the cable is short >enough to avoid ringing. That may be true in practice, but there is also no guarentee. We are discussing the problems of one particular person with his particular serial port. It may be that his problems are caused by his particular serial port NOT behaving in that way, even though it is a perfectly designed serial port. It may also be that this is a total red herring. >> way out of spec for the serial port. (Or with the typicallysmall duty >> cycle, more like -1V to 4V) _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
