PIC 16f877a

[CipiCips]

Hi

I have a very strange problem with PIC 16F877A, When I enter program into the PIC and plug PIC into circuit board and turn on the switch, everything is normal and work like it should work. But when I turn off the power and after few sec I turn it ON, PIC doesnt work corectly.

For example:
WHen I plug him after programing, my motors moves acording to AD conversion, but when I turn it off, and after a short period when I turn it ON, PIC reads another values from AD ?

thx

[mister_e]

Various thing may do that, but I would suggest to enable the Brown-Out detect, and Power On Timer config fuses and see how better/worst it is from there.

[aratti]

The schematic could help to understand better. Can you post it?

Cheers

Al.

[CipiCips]

HI

here is the schematic:



I have tried to enable BOD, and these are results:

When I insert PIC into Board and turn the switch on, program run correctly, but when I turn the switch off and let it be offline few min, then when I turn it on it want work, BUT when I turn OFF the switch and Take out PIC from board and Plug him back to board, and turn the switch ON program runs correctly ?
So every time I Remove it from board and plug him back program works

[mister_e]

Slow slope power-on/Power off PSU behaviour.

You want to test the BOR, PD bits at the start of the program then.

Check the datasheet for STATUS, PCON register

[CipiCips]

I am lil bit confused now ?? how to chack that ?

[aratti]

What is the state of all the unused and floating pins ? Are they outputs or inputs ?
If you have them set (tris setting) as input then turn them into output and clear them to zero.

Never leave inputs floating without pullup or pulldown.

Cheers

Al.