4x4 Hex keypad interfacing

[cyrrah]

hi.. i just want some advice/suggestion on what port will i interface my 4x4 he keypad.. im using pic877a.. i have port b & d available.. which port will i use? and how will i connect it? pls guide me

 

[cubanflyer]

You would look at some along these lines. But change the port used, in you case I would most probably use Port B

 

[cyrrah]

if ill use portB, do i still need pullup/pulldown resistors? if yes, at what pins will i put it?

can it be done without any external resistors? i just dont understand what's the use of resistors coz some layouts ive seen does not use it.. can you please enlighten be about this matter? thanks

 

[cubanflyer]

The resistors offer some protection against short circuit of the pins.

An example of what you would do with the above.

set pins B0-B3 as outputs, pins B4-B7 as inputs

Set B0 to high, check the inputs for key press and respond if required.
Set B1 to high, and check inputs & respond
Set B2 to hign, check inputs & respond
Set B3 to high check inputs & respond

There a few ways you could handle the above, depending on what you wish to achieve.