minimum pulse duration

[jon]

i need to record to a counter a number of pulses at a frequency of approx. 100hz, how long does the pulse need to be either "on" or "off" (in this case the decoder only produce a quick low state of 100us for each pulse) to be recorded by the PLC? by the way the 2 high speed counters are already used by 2 encoders...

thanks in advance!

[support]

If you have already used up the two channels of high speed counter then there isn't any more high speed channel left. You can only use the normal counter which require that the pulse width be greater than the worst case ladder logic scan time. The ladder logic scan time starts from a minimum of 2ms upward and can become quite long if you have custom function takes a long time to execute (such as communication or EEPROM save or load). There is no way the PLC can capture 100us pulse width. You'll need some circuit that will extend the pulse width or use a second PLC' High Speed Counter to capture this fast transition.

[plc_user]

Is it possible to achieve this with an interrupt?  Since the encoder channels are used up, could you not write alittle routine that would accumulate a count?

When interrupt occurs make a variable increase like
A=A+1

[support]

Unfortunately in the case of T100MD+, the 4 interrupt inputs are shared with the High Speed Counter (HSC) inputs, so since he has used up both channels of HSC there isn't any interrupt inputs left for implementing an interrupt-based counter.