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I am designing a project that contains several CMOS counter ICs (CD4017 specifically).

What is the state of the counter on power-on? Do I have to incorporate circuitry that pulls the reset pin high on power-on to ensure the counter starts at zero?

I checked datasheets from multiple manufacturers, and none of them mention this subject. I found several claims online that the state of the counter is unpredictable on power-on. However, I also found many projects which do not include a reset circuit, and the issue is not mentioned either.

The reset circuit adds complexity and additional parts, which I would like to avoid if they are unnecessary.

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You have to assume that if the datasheet doesn't specifically mention a power-on state, that the state of any digital logic is undefined at power-on, and you need to provide a reset pulse to get it to a known initial state.

Generally speaking, only single-chip microcontrollers implicitly handle power-up initialization. However, you can purchase tiny power-up/reset controller chips that will add that feature to any circuit.

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The initial state of most digital counters is unspecified. If your design requires the counter to start at zero, you must "manually" clear the counter after power-up.

In many applications the initial state of a counter is not important, as it will soon be reset during normal operation.

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    \$\begingroup\$ It may be worth noting that datasheets for non-binary counters sometimes specify count sequences from every state; something like a BCD counter might normally never go more than 9 pulses without reaching "9", but if it happened to start on "A" it might count A-B-C-D-0-1-2, etc. needing a total of 13 counts before the first time it reaches "9". Some kinds of counters if not reset might get stuck in a cycle which never reaches an "expected" count value. \$\endgroup\$ – supercat Dec 29 '14 at 18:25

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