I am a beginner in electronics. For a project I have to use five 4017 counter and I understood how they works: one of ten outputs is high at the same time.
But at some time, I need to set HIGH the 10 outputs of the five counters simultaneously. In your opinion, what is the best way to achieve that ?
I thought about using OR gates with one input set to HIGH after the counters but I can't find IC with more than 4 gates (CD4072B for example) so there will be a lot of OR gates on the circuit. Also, I thought about using diodes, is this a good idea or is there IC which can achieve what I want ?
Best Answer
There is an IC that can lend itself to this problem. Use a CPLD part or an FPGA to implement the logic of the five Johnson counters (4017's). Then change the logic to either add in a layer of OR functions at each counter output or change the fundamental design of each of the Johnson counters such that there is an "force all outputs high" mode.
If you look at the equivalent circuit of typical 4017 such as this one from an old Intersil / Renesas data sheet:
You will be able to get a good idea of the logic function to implement in the CPLD/FPGA. You will also notice that the "force all outputs high" (AOH) mode can be implemented simply as: