POWER-UP PROBLEM

[hundil]

hiiiii

I HAVE A MODERATE SIZE BOARD USING PIC16F877.
I USE A FEW DIFFERENT INTERRUPTS IN THE SOFTWARE.
(BUT, IT IS THE SAME IF I USE PROGRAMS WITHOUT INTERRUPTS)
I USE CCS COMPILER WITH THE VERSION
WHEN THE CIRCUIT IS POWERED-UP FOR THE FIRST TIME AFTER PIC IS PROGRAMMED, EVERY THING
IS OK. IF IT IS POWERED DOWN AND POWERED-UP AGAIN, IT IS NEVER WORKING ANYMORE.

WHAT MAY THE REASON BE ?

IF IT IS TURNED ON BY AC PLUG SWITCH, IT IS NOT WORKING
BUT, IF APPLIED DC POWER SOURCE BY A CONNECTOR DIRECTLY, IT IS ALMOST OK.

ADDITIONALLY, IF I PUT THE BOARD ON A CLEAR PAPER SHEET NORMALLY, I CAN NOT SEE ANY CHARACTER
ON LCD. (EXCEPT A DARKED FIRST LINE)
BUT IF I PUT THE BOARD WITH PIC16F877 VERTICALLY (!) , IT IS WORKING PROPERLY.

WHAT DO YOU THINK THE PROBLEM IS?
IS THAT MATTER JUST FOR PIC MICROCONTROLLERS?
WHAT SHOULD I DO?


THANKS...

hundil

[hundil]

There is a 100n capacitor connected to the out pin of 7805 regulator, even
it (100n) is very near to VDD and VSS pins of PIC16F877.

HELP...........

[rnielsen]

First, make sure you have MCLR tied to VCC through a resistor. Next, if you are not doing any in-circuit programming make sure you have NOLVP in your #fuses statement. This one bit me for a while until I learned about it.

[future]

Try adding #zero_ram directive

[Ttelmah]