[SOLVED] PIC16F716 Oscillator Problem - Simple LED Blink

[Mywk]

Hey all, new here so please no flaming just because I'm newbie in what concerns to electronics, I'm just a programmer trying to learn.

16V -> Diode -> 5V Voltage regulator -> Pic VDD
4Mhz Oscillator I found from spare parts correctly connected to port 16/15
Led + to Port B2

Here is the code I'm using:

#include <16F716.h>
#fuses XT,NOWDT, NOBROWNOUT
#use delay(clock=4000000)

#byte PORTB = 6 // PIC16F62X Data Sheet, Bank0

void main(void)
{
 set_tris_b(0);
 PORTB = 0;
 
 while( 1 )
 {
  output_high(PIN_B2);
  delay_ms(200);
  output_low(PIN_B2);
  delay_ms(200);
 }
}

It sometimes did work when I had my finger above the Microcontroller (static?), but since i tried 3 different ones I don't think that is the problem.


I tried to use a PIC16F628 and it works without any problem, basically same ports/connections, here is the 628 code:

#include <16F628.h>
#FUSES NOWDT,NOPUT,NOBROWNOUT,NOMCLR,NOLVP,XT  //INTRC_IO (Not using internal clock)
#use delay(clock=4000000)

#byte PORTB = 6 // PIC16F62X Data Sheet, Bank0

void main(void)
{
 setup_comparator(NC_NC_NC_NC);
 setup_vref(FALSE);
 set_tris_b(0);
 PORTB = 0;
 
 while( 1 )
 {
  output_high(PIN_B2);
  delay_ms(200);
  output_low(PIN_B2);
  delay_ms(200);
 }
}

What could be the problem? Maybe the configuration of the Fuses?

Thanks In Advance!

 

[mister_rf]

Along with the crystal, connected to the GND, two ceramic capacitors (of approximately 22 - 27 pF) will be required for this job. See details:

 

[Mywk]

Along with the crystal, connected to the GND, two ceramic capacitors (of approximately 22 - 27 pF) will be required for this job. See details:

I completely forgot to say that I already have two 25pF capacitors correctly attached to the circuit, otherwise I think it would not even work with the PIC628 right?

--Edit: Just noticed, sometimes I plug it to power and it runs for like 3~4 seconds, then stops.

 

[mister_rf]

What about MCLR (pin 4) connected to the VDD via a small 10k resistor?

---------- Post added at 23:14 ---------- Previous post was at 23:11 ----------

And by the way, to protect the PIC use a series resistor for the LED. (100- 220 ohms)

 

[Mywk]

I added a 200ohm resistor before the led not to burn it just now.

That worked like a charm!! Why?
Also, is the 10k resistor really needed between MCLR and VDD? Why?

Thanks, that was a great help!

 

[Kurenai_ryu]

MCLR requires a high state to work and low state for reset the micro... with no pull-up (10kohm to VDD) it's in no definite state so with your finger it goes to high or not... mostly static and so....

---------- Post added at 17:11 ---------- Previous post was at 17:06 ----------

never forget to set a pull-up to MCLR, VDD to 5V GND to 0V the crystal

and also a common led works with 2.4V 5mA (not exact data but it works) so if you give it 5V it's certainly it will be burned or at least will heat... with a 200ohm resistor you limit the current to almost 13mA (5-2.4 = 2.6/200ohm == 13mA just a little high) but also it depends on your Led, i would set a 330ohm or higher (up to 1K) resistor for any led in my circuits...

---------- Post added at 17:12 ---------- Previous post was at 17:11 ----------

aaaannnnd also Don't forget that a common IO pin in a PIC at most can draw or source 20mA of current... so don't push it too far....

 

[Mywk]

Thank you all, very useful, replaced my 200ohm led resitor with a 1k one, also MCLR doesn't seem to do anything different whenever I use the 10k resistor, a 400ohm resistor or directly connected.. Then what do you mean with the high/low state?

Thanks once again!

 

[mister_rf]

MCLR/VPP = MCLR and VPP are two functions on the same pin;

MCLR means Master Clear, and functions as the Reset pin on the PIC micro, causing the PIC to be held in a reset state as long as MCLR is at 0 volts. When MCLR is connect to VDD instead, then the PIC begins running by executing the first instruction in program memory.

VPP means Voltage for Programming. When there are 9-12V ( need to see the specific datasheet) on this pin, the PIC goes into a special reset state where it's not running, but it can be programmed.

 

[Kurenai_ryu]

MCLR/VPP = MCLR and VPP are two functions on the same pin;

MCLR means Master Clear, and functions as the Reset pin on the PIC micro, causing the PIC to be held in a reset state as long as MCLR is at 0 volts. When MCLR is connect to VDD instead, then the PIC begins running by executing the first instruction in program memory.

VPP means Voltage for Programming. When there are 9-12V ( need to see the specific datasheet) on this pin, the PIC goes into a special reset state where it's not running, but it can be programmed.

right!

it's always recommended to put a pull-up resistor at MCLR, you can use a higher res up to 47kohm or lower even directly to VDD

but

if you plan to put a RESET push button, you can´t put MCLR directly to VDD, so it should have a pull-up ressistor... this resistor shouldn't be too low so the current while pressing the button shouldn't be too much...

also leaving it with no pull-up could make it very vulnerable to static and noise...