I would like to connect a Quadrature encoder to a T100MD-888+, say 128 PPR, to HSC[1] and also feed one of the A or B signals into pin #5 as Interrupt Channel #3. This would allow me to synchronize reading A/D signals to every ( maybe ) rising pulse of the encoder.
The ISR ( Interrupt service routine ) would read 4 analog channels, and the value of HSC[1], do some processing, and then display the results on an LCD.
From an earlier discussion on timing, the moderator said
"The minimum scan time of the PLC is therefore = logic scan time (approx. 10us per word) plus I/o scan time (minimum 2ms)."
So if a program was say 1600 words long, I would expect a total period for one interrupt at 1600 x 10 us + 2 ms = to about 18 ms.
This would give me a maximum of say 50 interrupts per second.
What happens when the PLC see's incoming Interrupt pulses at a rate greater than 50 hz?
Is the interrupt input disabled when the ISR is processing, ( non retrigerable one shot equivalent ) and then re enabled when the routine is complete?
In other words, if the Interrupt is coming in at 150 Hz, will we still see a 50 hz. throughput, or will some error occur, and halt the PLC?
Your assistance is appreciated