4538 monostable input rise/fall restriction

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with an
inverter at one of the OR inputs.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.

 

"Jim Thompson"

Oops! I had another look at the datasheets by TI and RCA
(really the same) and they say that the inputs have Schmitt
triggers. Don't know how I missed that. Thanks for pointing
it out. NatSemi and Fairchild don't mention it.

Question answered above^. Anyway, what I want to do is this:
One monostable is triggered first to produce a pulse of ~50
msec. The second mono is triggered a little later while the
first one's Q output is still high, that is, before it has
reverted to the idle state. It doesn't matter if the second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence. The
two outputs go to different sections of the overall circuit.

 

Probably a manual switch - a momentary tactile type. The
design is still in the early stages and many factors are not
yet clearly defined.

 

Yes, that's exactly what I had in mind. What I didn't know
when I made my opening post (because I missed seeing it in
the datasheet) was whether the mono trigger inputs have a
Schmitt trigger that accepts slow rise times.

 

The first monostable *was* intended to set up a circuit
before and during application of the pulse from the second
mono. But I've changed the design of the controlled circuit
so that, although the mono pair will still be used, they now
work independently and sequential triggering is no longer
needed. What I didn't mention before was that the second
mono was to have the option of either manual direct
triggering or being triggered by the first mono.