Keypad interface in pic16f877

[ecaits]

Dear All,

To interface keypad in pic16f877, will I need to connect +Vcc with resistor to input port to detect the switched pressed???

Can you give me logic of key detection???

Thank you

 

[techgreed]

A high read at pin P0.0 indicates switch S1 is open and a low indicates switch is closed.

 

[betwixt]

It depends entirely on how you have connected the keypad. Techgreeds example shows how to do it with individual switches (note the '877 reset works the other way around) but not if you have a keypad in a matrix.

The general rule is the input pins must be held in their 'inactive' state until a key is pressed and this *may* require the use of an external pull-up or pull-down resistor depending on how you wire it up and drive it. What you must never do is leave an input floating until a key connects it to something, that would result in random signals. Some of the pins on the '877 have internal pull-up resistors which you may be able to use to save components.

Brian.

 

[Gorgon]

First of all, when you say keypad are you thinking of a matrix? If so, how many keys in the pad? How many keys in total?
How many pins are available on your PIC for this keypad interface?