SN74LS92 frequency divider

Sebastian-Richard Ene

Joined Oct 9, 2018
7
Hello, I have a question. How can I use the SN74LS92 IC to design a frequency divider with value 11 ?
I know it has a 12 frequency divider but how can I make it divide by 11 ?

MrChips

Joined Oct 2, 2009
28,471
You need to design a decode circuit that resets the SN74LS92 when a certain terminal count is reached.

bertus

Joined Apr 5, 2008
22,138
Hello,

How do you want to count?

The 92 is missing some steps between 5 and 6.

Bertus

Sebastian-Richard Ene

Joined Oct 9, 2018
7
Hello,

How do you want to count?

View attachment 173033
The 92 is missing some steps between 5 and 6.

Bertus
I don't understand. It's my first experience with frequency dividers and i'm a bit confused. I suppose I would use the LS92

MrChips

Joined Oct 2, 2009
28,471
74LS92 is actually two stages in one.
One stage is a divide by 2 counter. The other is divide by 6.
You only need to decode Q2 and Q3 into an AND gate followed by a flip-flop if you want to delay the reset function to the next clock pulse.

Sebastian-Richard Ene

Joined Oct 9, 2018
7
So basically I have to make the counter count 0-10 instead of 0-11 ? that way it makes the frequency divide by 11 ?

MrChips

Joined Oct 2, 2009
28,471
So basically I have to make the counter count 0-10 instead of 0-11 ? that way it makes the frequency divide by 11 ?
You got it.

Joined Mar 10, 2018
4,057
There is a problem with the reset approach. If you want
it to divide by n then the approach where you decode n
(it counts 0 to n-1) means that it counts 0 to n-1 "normal"
then when its outputs flip to next value, n, it then executes
reset. But notice it had to go to n to do it, although it stays
in this state only a short period of time. So looks like a
glitch on the outputs.

Additionally when you execute the reset the decode output
in just a few nS goes away, which may violate the reset pin
hold time.

This is a problem in asynchronous systems where the above
produces some in determinate timing and can violate chip
timing. one approach is to use synchronous counters.