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I'm looking at using a CD4031 as a digital delay line in a project I'm working on. In this project, I'd much rather said digital delay line power up in an all-0 state, lest errant 1s clocked out of it cause the output to turn on something that it shouldn't at that point in time. That said, the CD4031 does not have a reset pin available. What was done back when this IC was regularly applied to deal with/ensure that it had a standard powerup state, or was that simply not a concern in the applications it was intended for?

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  • \$\begingroup\$ Ignore first 64 clocks or disable use until 64 clocks have occurred. \$\endgroup\$ Oct 1, 2022 at 16:51
  • \$\begingroup\$ These devices were used, back in the day (1980's), for things like 'range-finders' among other things. Often, a start pulse was provided that triggered clearance using 64 clocks at 12 MHz (less than 6 us.) During that short period, the circuit provided an output pulse that covered this 'dead-time' for outside circuits to observe. \$\endgroup\$
    – jonk
    Oct 1, 2022 at 21:03

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If the unknown initial state is a problem, then external circuitry is needed to make sure the initial state is not a problem. It depends on what initial state is needed, like keeping the whole system in a reset state, or clock in an initial state.

It might be anything like just gating off the output while a reset signal is active, or not using the output in the next stage if reset is active. It can also clock in zeroes or any other initial pattern you want.

But it would be clear that the reset would need to last at least 64 clocks so that you get out the required state or ignore the invalid outputs.

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One way would be to run the clock continuously and simply feed zeros in there for >64 clocks (and inhibit the output with a gate). It could just be a crude timer or it could be a 6 bit or more counter.

And for some applications, the initial state may not matter, just inhibit the output until it's filled with valid data.

A bit surprising that part is still shown as active (and has made it to TSSOP packaging). There must be some applications.

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