16F819 - Pullup on MCLR required?

[Kamikaze47]

Ive just started playing with a 16F819, and I notice that pin 4 is RA5/MCLR/VPP

How can this pin be used for I/O, doesnt the MCLR need a 10k pullup resistor to +5v in order for the PIC to operate?

[Dwayne]

the pin has a internal pullup...

Set your programming fuse to activate this, and you will not need a pull-up resistor.

Dwayne

[Kamikaze47]

ok, so if its got an internal pull-up, wouldnt that still mean that if i pull the pin low, the pic would reset?

if so, how can this pin be used for I/O ?

[Bruce]

On PICs with the option of using /MCLR for an input, you enable or disable the reset function using the config word.

If you're using the default PM assembler you can add config options to your code to over ride defaults in the device header file.

@ device mclr_off, xt_osc, wdt_on, pwrt_on, lvp_off, protect_off

Or you can just disable /MCLR with you programmer software before programming the part.

[Dwayne]

the MCLR is a pin that you can use to reset, or activate your chip.

You have a fuse that you can use to make it pull high, so that you will not need to attach it to 5 V postive.

If you do not activate this fuse, your chip will need this 5 volts positive to run properly. If you forget to activate this fuse and not attach the pin to 5 volts, your chip will run spuratically, will be unreliable, and will shut off on you unexpectedly. Sometimes just touching the chip will turn it on or off.

Bruce gave you the programming fuse command for the chip. That will help you out.

Dwayne