# What circuit will output a short latch pulse when the clock input pauses?

I'm transmitting serial data across a cable to a shift register. I transmit data in discrete packets, where different packets have different bit lengths. The clock frequency is about 20 MHz while transmitting.

When each packet ends, I need to generate a short pulse to latch the shift register. I know a packet has ended when the clock stays low for a few cycles.

What circuit will output this latch signal?

• The shortest packet is 800 bits, for a duration of 40 μs minimum.
• Idle time between packets is 10 μs minimum.
• The latch pulse duration must be 10 nanoseconds minimum.
• 1) Is the clock rate known, or at least constrained? Jan 5, 2020 at 22:32
• 3) Do you need a pulse, or would just a rising or falling edge suffice? Jan 5, 2020 at 22:41
• a re-triggerable monostable multivibrator (retrig one-shot) would be the kind of circuit that you are looking for Jan 5, 2020 at 22:56
• 1st you must be more specific. T1= Duration free of clock transitions ,T2 for duration of pulse and recurring if necessary. With tolerances.. even if you don’t care.... Jan 6, 2020 at 0:01
• you want a missing pulse detector Jan 6, 2020 at 2:34