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cd4026b: How to use the CD4026B "Ungated C segment" pin

Part Number: CD4026B
Other Parts Discussed in Thread: SN74LVC1G97, SN74LVC1G74

Hi !

I'm really puzzled about a practical use of the CD4026B "ungated C segment" pin.

From the datasheet, I understood that this pin goes low when the output is relative to the "2" number. Ok.

Also in the datasheet it's said that this pin may be used in certain divide by 12 and divide by 60 counters.

Does anyone have a working circuit like a 24h digital clock using this output pin ?

Thanks in advance !

  • Hello,

    From what i can tell in the Figure 3 timing diagram, the display enable in is used to ensure that (if you want to do divide by 12) the ungated C output so that when you get to the 10th count, it will only show a single LED in the bottom right corner where the c segment is, to show that it is not counting by 10s, but rather 12s in this case.

    This count, coupled with the carry out, which every 5 times it counts to twelve will return back low, can be used to get a 5*12 = 60 counter.

    Hopefully this makes sense, it actually took me a few minutes to try to figure it out also.

    Best,
    Michael
  • Hi,

    Thanks for the reply !

    I'm not sure if I've got the idea. Isn't the display enable in /out function to blank non significant digits ?

    From the timing diagram I see that the UGS signal is periodic every 10 clock cycles, not 12. I'm missing something.
  • Do you have any circuit diagram showing how to do this ?
  • Hello,

    I looked at this for quite some time, and to be honest, was not able to come up with a good solution for how to use only the device to do a 12 or 60 bit counter.

    I was able to come up with a solution that I believe works for 12 bit counting using some external devices.

    Please see the image I drew up attached.

    This circuit will reset the counter at 11 back to 0, so that it is counting by 12's. It allows the reset to trigger once it gets to 10 and then actually generates a pulse at 11.

    The Flip flop would be an SN74LVC1G74 and the AND gate with one input inverted would be the SN74LVC1G97.

    The only extension of this that i can think of to get to 60 would be a counter that counts up to 4 (from 0) based on the rising edge of the carry out and then doing a similar circuit to reset that counter.

    I don't see an obvious solution as to how to use only this chip to do 12 and 60 bit counting, i think additional circuitry is required.

    Best,
    Michael

  • Hi Michael,

    I've reached a similar solution, your solution should work, but it's far more simple to use some standard gates connected to the decoded outputs to do the job, or even a magnitude comparator.

    The first time I had contact with the 4026 was in 1986 at the university. The device was made by RCA and I never figured how to use this obscure output neither found ANY clue about how to use it.

    There are some funny quotes on the internet about it:

    from the datasheet

    "When the DISPLAY ENABLE IN is low the seven decoded outputs are forced low regardless of the state of the counter. Activation of the display only when required results in significant power savings. This system also facilitates implimentation of display-character multiplexing.

    The CARRY OUT and UNGATED "C SEGMENT" signals are not gated by the DISPLAY ENABLE and therefore are available continuously. This feature is a requirement in implimentation of certain divider functions such as divide-by-60 and divide-by-12."

    One of the quotes:

    "I'm wondering if there is a sadistic sense of humor by a TI engineer way back when. Guess I'll use the segments.

    Still, I have to wonder what the heck they were thinking with the "Ungated C segment"."

    Thanks anyway, I really appreciate your effort.

    Best regards,

    Antonio

  • Hello,

    Feel free to post your solution for others here on the forum, so we have a more optimal solution and can share with others when they search for this application.

    Thanks!
    Michael
  • Here is a 24h clock with the 4026 not using the gated c segment.

    http://danyk.cz/hodiny.png

    I'll do some more research about this obscure signal and post any update here.