Good day. I have a question in regards to the 4017 counter ic. I understand the reset pin needs to be low for counting to proceed and high to reset, however I have a circuit in mind that I would like to do that uses the 4017 to process short pulses. I need it to be reset for each pulse and the outputs will vary from pulse to pulse. I believe the counter will not function if reset is held high once switched from low. On the data sheet, there is min. reset pulse width of 200ns or so and a min. reset removal time of 400ns. My question is this. The min. pulse seems to be the length of switch signal needed to activate reset, however I'm not sure how to interpret the removal time characteristic. Is this akin to a 'fall time' length or some other parameter needed to transition the reset pin? A detailed explanation would be most valuable since this would be a faster circuit using 'us' and 'ms' switching times. Thank you.

 

On the data sheet, there is min. reset pulse width of 200ns or so and a min. reset removal time of 400ns. My question is this. The min. pulse seems to be the length of switch signal needed to activate reset, however I'm not sure how to interpret the removal time characteristic. Is this akin to a 'fall time' length or some other parameter needed to transition the reset pin?

The min. reset removal time is the maximum time after the reset goes low, before it will reliably start to count input clock pulses.
In other words, you should not apply any clock pulses you want to count until at least 400ns after the reset pulse goes low.
Make sense?

 

Makes perfect sense. Thanks again for your help. May I ask just to get confirmation that the best option for resetting short pulses would be to add a small capacitor from pulse signal to reset pin and have a pull down resistor from reset to ground?

 

that the best option for resetting short pulses would be to add a small capacitor from pulse signal to reset pin and have a pull down resistor from reset to ground?

Not sure what you are asking.
Is the reset pulse too short or too long?

 

Sorry for the poor description. The schematic and idea are at home. I'll try to give a clear mental picture. I'd like toggle the outputs of the counter with the same pulse used to pull reset high and clock inhibit back low to resume operation. Assume there was a previous counted pulse that froze clock inhibit on an output. This new pulse (between 150us - 25ms) would reset and activate the counter, then freeze on an output when the pulse was over. So I need the reset to switch as fast as possible in order to count the pulse duration as accurately as possible. So I thought the pulse going through a capacitor til charged for a few hundred nanoseconds or so to 'reset' would bounce the reset fast and lose only a fraction of the pulse time for counting. Hopefully that made sense. If not, no worries and thank you for the answer.

 

So I thought the pulse going through a capacitor til charged for a few hundred nanoseconds or so to 'reset' would bounce the reset fast and lose only a fraction of the pulse time for counting.

Then yes.
A series capacitor with a resistor to ground would shorten the reset pulse.
The effective pulse width (to the 50% point) is about 0.7RC.

 

You're awesome. Cheers.