[oopic] Re: Angle of attack VII - any help appreciated

--- In oopic@yahoogroups.com, "Nick Mulder" <nick.mulder@...> wrote:
>
> Okidoki,
>
> Locally (and cheaply) I can get the 74HC160 Synchronous Decimal
> Up/Down Counter - http://www.jaycar.co.nz/products_uploaded/ZC4855.pdf
> - It seems to be the same chip aside from the fact it is BCD and not
> the full 2^4 bits

Better check page 2 of 12 where it states that the Clear input is
asynchronous. However, the Load' input is synchronous. All you have
to do is load a value of 0.

>
> Now if I'm understanding correctly it should work fine but I need a
> different setup of logic doohickeys for the reset and 13th(12th)
> outputs ?
>
> Either that or maybe:
> http://www.jaycar.co.nz/products_uploaded/ZC4864.pdf - which is a
> different beast but in the same ballpark ?

Again, this chip also has asynchronous clear. Unfortunately, it also
has asynchronous load.

Since you only want an output every 12 or 13 pulses, you can use a
single counter (74HC163) and a D flop such as the 74HC74. What we can
do is count 1..12 (12 count) or 0..12 (13 count). We generate the
LOAD' (PE') signal by NANDing Q3 and Q2 (12). We ground the D3, D2 &
D1 inputs and connect the D0 input to the Q output of a D flop. The D
input of the D flop is the Q' output of the flop and the clock is the
LOAD' signal.

Assume the D flop is reset. The Q output is 0 so when the counter
reaches 12, the counter will load with 0 and the D flop will toggle.
When the counter reaches 12 (13 clocks later) the Q output will be one
and the counter will load with 1. The Q output of the D flop will
toggle back to 0 so that 12 clocks (counts 1..12) later the counter
will be loaded with 0 again.

Richard

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