Strange Problem with 16F877A Led Blink Demo!

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Hello Dear All,

I had some problems with 16f877a, therefore, I decided to try a simple led blink demo on it.

Unfortunately, the led does not blink or blinks very quickly. I tried some different 20Mhz crystals and 4Mhz crystals. Moreover I tried some different pins; A0, C0, D0, D1... However it couldn't solve the problem. I created a new project for 16f690, pasted the same code into it then, it worked properly on 16f690.

I know that Proteus ISIS simulator is not so reliable but I want to say that, I don't get such a problem on ISIS.

I will be very glad if you can help me.
I use PCWHD 4.120.

main.c:

[Ttelmah]

1) You have got a series resistor between the PIC and the LED?.
2) How are you building this (PCB, breadboard, stripboard etc.)?.
3) Give a part number for the crystals - must be parallel cut type, or may run wildly off frequency. What loading capacitors are you using.

Best Wishes

[blueprint]

Thanks for your reply Ttelmah.

1. I have a 330 ohm resistor between the pic and the led.
2. I try the circuit on a breadboard. I am sure that connections are ok. I checked them with a multimeter. Moreover, I tried another breadboard.
3.I can give part numbers of them in a short time, but, these crystals work with 16f690 and 18f2550. I tried 15pF and 33pF capacitors.

[Ttelmah]

Ok.

Pullup on MCLR?.

In the code:
Change oscillator to XT for the 4MHz crystal.
Look at what else is on pin A0:
add:

SETUP_PSP(PSP_DISABLED);
SETUP_ADC_PORTS(NO_ANALOGS);

at the start of main.
Some chips wake up with some pins defaulting to analog. Might be your problem.

Best Wishes

[PCM programmer]

I made your code into a test program, and compiled it with vs. 4.120
and ran it on a PicDem2-Plus board (red vs.) and it works. I had to
jumper from pin A0 to pin B0, because PicDem2-Plus has an LED on
pin B0. But it works, the LED blinks at a 1 Hz rate, 50% duty cycle.

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