Re: Counting 1-6 instead of 0-9 with a 74LS192 / 74LS47

On Thu, 29 Sep 2005 19:42:54 -0700, Bob Monsen
<rcsurname@xxxxxxxxxxx> wrote:

>On Thu, 29 Sep 2005 22:25:28 +0000, Rikard Bosnjakovic wrote:
>
>>
>> Also, I have no real clue yet how to start on number 1 instead of 0.
>> Adding 1 to 0 would ofcourse do it, but my knowledge is still too limited
>> to see an immediate solution for this particular problem.
>
>The 74LS192 has a parallel load function. So, you hard-wire the parallel
>load inputs to equal binary 1, and instead of doing a reset with 0111, you
>use it to load the counter. Sadly, the load function is active low, so you
>need a 3 input NAND gate for the load function.
>
>I haven't tried this, so I don't know if there are strange glitches.
>However, for your application, I suspect they'll happen so fast you won't
>notice them.

---
The 192 has an asynchronous parallel load, so there _will_ be
glitches in the NAND's output which will load the 192 at unexpected
times. The solution is either to buffer the output of the NAND with
a "D" type flip-flop or to switch to a counter with a synchronous
parallel load, like a 161 or 163.

A serendipetous result of doing it that way is that the circuit's
POR will set the output of the counter to zero on power-up,
capturing the first count acuurately as '1', and thereafter will
roll over to '1' inxstead of '0'.

Also, he can use the AND he has now and get the inversion he needs
for the load from the flip-flop's Q\ output.

--
John Fields
Professional Circuit Designer
.

Relevant Pages