I trying to implement a 4 buttons keypad using interrupts. should I connect the push buttons directly to the ISRs or should I use PWMs connected as one shots to the ISRs?

Neither - use the debouncer component (under digital/functions), and connect that one to the ISR.

I was tought NEVER to connect an interrupt directly to a mechanical switch since that may lead into troubles caused by bouncing.

Bob

 ok thanks :)

Take a look at this for GPIO interrupt discussion www.cypress.com/

The debouncer usage discussion in datasheet suggests the following -

When to Use a Debouncer

A Debouncer component can be used to debounce the input digital signal from most types of
switches. Since it does a lot of work that could otherwise be done by firmware, it can be used
when a firmware-based switch debouncing solution is not practical.

Basically its pretty easy to debounce in firmware a pin generated interrupt, so if you are

concerned about total HW usage consider that as an approach. Uses no HW cells or routes.

Regards, Dana.

... and of course I would like to introduce my "Making of a Keypad" elaborate. Bit old, but still working...

Dive into it here : http://www.cypress.com/?app=forum&id=2492&rID=68603

Bob

"I was tought NEVER to connect an interrupt directly to a mechanical switch since that may lead into troubles caused by bouncing."

I too have heard that before, and in general I use firmware to debounce.

But then if you examine what our peers have told us, re no mech sw to an interrupt, implication

is ISR rate potentially too high, you run up against the facts, mechanical that is, and contact inertia

causing relatively low rates. All the scope captures I have ever seen put those rates in the 10's of

uS to 10's of mS rates. In a 1 MIPs processor that was probably an issue. The other problem is if mech

sw input is used as clock or as data failing to meet Ts and Th times, but edge triggered ISRs pretty much

take care of that.

So in short I think the idea was born out of level triggered ISRs, slow cpu's, and a little fllooby dust thrown in.

That being said I think most of us still use firmware to handle.

Regards, Dana.

"I was tought NEVER to connect an interrupt directly to a mechanical switch since that may lead into troubles caused by bouncing."

Same here.

I guess debounce routine is one of those that we learned to write when we start our programming job. Because the boss always say that hardware increase prodcution cost, and software is not.

Although there are several aproaches to de-bouncing I found some that will run questionary under bad conditions especially aging.

Or haven't you got some "old" equipment where the keys do not come up as pressed or come more than once? Despite a brokencontact this could be an indication of a, well, not-as-good-as-it-could-be debouncing method.

Bob

 thanks :)