Clock problem on 16f84

Wridmuld · Joined: 02 Apr 2004 Posts: 15

Hi.

I have written a short and easy part of code just to test if my 16f84 is alive. Three diodes blinking...

However, it's not alive.
Now I measured the voltage on the clocks (clkin and clkout) and they are both 0V.

How does this come? Anybody got any suggestions?

Wridmuld · Joined: 02 Apr 2004 Posts: 15

Erm - I might add that I'm not totally new to this. I have done a few projects on the 16f84. It's just that I have never before experienced that nothing happens at all.
I have tried with 3 different 16f84's, and I just can't believe they are all dead.

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

Wridmuld · Joined: 02 Apr 2004 Posts: 15

A simple LED flash program is just what I have made.
I have no logic probe. :(

It's just completely dead.

Ttelmah · Guest

Humberto · Posted: Thu Sep 30, 2004 8:06 am

Hi Wridmuld,

We would like to know a little more:

1) The #fuse configuration.
2) If you are using a Xtal, the value that has stamped on it.
3) The capacitor values involving in the oscillator circuit.
4) Did you test with another microcontroller ?
5) Post your test program.

Best wishes,

Humberto

Wridmuld · Joined: 02 Apr 2004 Posts: 15

Here is my code:

#device PIC16F84
#use delay (clock=4000000)
#fuses xt, nowdt
#byte port_a=0x05
#byte port_b=0x06

main()
{
int readval_b;
int readval_a;

set_tris_a(0b00000011); //A0-A1 INPUTS, THE REST OUTPUTS
set_tris_b(0b00001111); //B0-B3 INPUTS, THE REST OUTPUTS

while (1);{
port_b = 0x10;
delay_ms(500);
port_b = 0x00;
delay_ms(500);
port_b = 0x10;
delay_ms(500);
port_b = 0x00;
delay_ms(500);
}

delay_ms(1);
while(1);
}

I'm not sure what Xtal means, but I got a crystal. It's a 4 Mhz crystal and it says 4.00 which stand for Mhz, of course.

The capacitors are built into the crystal, so there should be no problems with that. And it has worked before.

I have tried 3 16f84 now, and as I said before, I doubt that all 3 of them are broken.

I am not sure what all the fuses mean, tbh.

/Wridmuld

jpa · Guest

while (1); {

The ; should not be present. while(1); is an endless loop. The program nerver goes to the next instruction.

Humberto · Posted: Thu Sep 30, 2004 10:33 am

Hi Wridmuld,

That´s the way, posting your test source and complete info.
As jpa remarks, just take out the ; following the while

For an endles loop you can use

Wridmuld · Joined: 02 Apr 2004 Posts: 15

Erm...hrm.

This was a little embarassing actually. Now it works! Embarassed

But a question still: the fuses - how are they to be used? How many fuses are there and what is the purpose of them?

Humberto · Posted: Thu Sep 30, 2004 12:15 pm

The compiler need to know about the hardware to set accordingly a special register named
Configuration Register, wich is accesable only during programming time.
The directive #fuses tell the compiler to set each bit of the referenced register.
In the 16F84 datasheet you will find all the info regarding this register and the meaning of each bit.

Following is another way to write your test: