I am building this project where I have to use presettable BCD up down
counter 74ls192 but that IC is not available in my country... Instead
74LS190 is available.. How can I configure it to work the same???? I am
from a small asian country, NEPAL... Can anyone help me out??? the
circuit I am building is the watchman watcher which uses this counter
to count how many times the watchman has missed the call... its at
http://electronicsforu.com/electronicsforu/lab/ at no.. 54 .. don't
hesitate to help me.. its my 2 credit project..

It looks like there are two problems. One is that you don't have a
"clear" input on the 74LS190, and the "clear" on the 74LS192 is used in
the circuit. But you can use the "load" input, with the A,B,C,D inputs
set to zero to accomplish the same thing. Be sure to think about
whether the clear takes place when the input is high or low, and
whether the load input behaves the same way.

The other problem, of course, is that the '190 uses a single clock
input, and an UP/DOWN selection, instead of separate UP and DOWN
clocks. Since this is apparently a school project, you should expect
to do a little thinking, and then you will learn more. Try to think of
a very simple logic circuit, which has two inputs (up clock and down
clock) and two outputs (up/down, and clock) that will accomplish what
you need. One thing to be careful about: how long before the clock
signal comes must the up/down input on the 74LS190 be stable? That is,
if the clock comes just when the up/down signal is changing, the
74LS190 may get confused. "Do I count up, or do I count down?" So you
want to make sure the clock comes only after the up/down is stable.
What do you do if an UP clock comes at the same time as a DOWN clock?
Should that ever happen in the circuit you are building? COULD it ever
happen?

If you think about all this, and still have questions, please post
again. Most people here won't want to just give you the answer, but
will want you to think about it yourself. We are quite willing to give
you ideas to get you started thinking, but it's from the thinking that
you will really learn.

Cheers,
Tom


shashwat wrote:
I am building this project where I have to use presettable BCD up down
counter 74ls192 but that IC is not available in my country... Instead
74LS190 is available.. How can I configure it to work the same???? I am
from a small asian country, NEPAL... Can anyone help me out??? the
circuit I am building is the watchman watcher which uses this counter
to count how many times the watchman has missed the call... its at
http://electronicsforu.com/electronicsforu/lab/ at no.. 54 .. don't
hesitate to help me.. its my 2 credit project..