PIC18F2431 Running Super SLow!!

[Philip Biebach]

Basicly I have a Pic18F2431 Setup connected to 3 LEDs, I wrote a really simple program that should simple flash the LEDs. At First I thought that the Pic had simple locked up and wasent executing any code but after letting it sit For a few mins i noticed it had switched to the nexts sequence of LEDs, After observing it over several tens of minutes i now discouvered that it does what the code tells it to but at a super slow rate.


the 3 LEDs are On PORTA.0, PORTA.1, PORTA.2

;Setup procedures
@ __CONFIG _CONFIG1H, _OSC_IRCIO_1H
@ __CONFIG _CONFIG3H, _MCLRE_OFF_3H

DEFINE OSC 8
ANSEL0 = %00000000
TRISA = %11110000
TRISB = %10110011
TRISC = %11110000

PORTA = %00000000
PORTB = %00000000
PORTC = %00000000

;Pin assignments
Symbol LED1 = PORTA.0
Symbol LED2 = PORTA.1
Symbol LED3 = PORTA.2

main:

LED1 = 0
LED2 = 1
LED3 = 1
pause 500
LED1 = 1
LED2 = 0
LED3 = 0
pause 500

goto main

[Melanie]

Datasheet!!! Page 28, Section 2-2 OSCCON Register... I don't see you setting it for 8MHz...

OSCCON=%01110010

Try adding the above before your TRIS statements...

For frequency critical applications, I'd also follow that with...

WHILE OSCCON.2=0:WEND

This ensures that program continuation is halted until the Oscillator is stable...

[Philip Biebach]

Thanks Melanie, it must have been defaulting to 31Khz or something

and i did check the datasheet(many times) just the wrong places, i was somehow convinced it had something to do with the AD Converters

thanks again

[Squibcakes]

Mel,

I've the reverse problem. Couple of questions if you don't mind:

I want to toggle the LED once a second running at a clock freq of 31.25kHz is this possible?

If I set the OSCCON to a freq of 2MHz (or lower), and I set DEFINE OSC 2 (or lower), my code wont compile?

Do you need to DEFINE OSC "speed" when using OSCCON? It seems that I do, eg the toggling LED seems to double in speed if I don't DEFINE the oscillator speed.

Heres my code.


' FLICK LED ON/OFF EVERY SECOND

' =============
' PRESET FUSES
' =============
@ DEVICE pic16F88, INTRC_OSC
@ DEVICE pic16F88, WDT_ON
@ DEVICE pic16F88, BOD_ON
@ DEVICE pic16F88, PROTECT_ON
@ DEVICE pic16F88, MCLR_ON
@ DEVICE pic16F88, WDT_ON
@ DEVICE pic16F88, CPD_OFF
@ DEVICE pic16F88, LVP_OFF
@ DEVICE pic16F88, CCPMX_OFF
@ DEVICE pic16F88, DEBUG_OFF
@ DEVICE pic16F88, PWRT_ON

' 000 = 31.25 kHz
' 001 = 125 kHz
' 010 = 250 kHz
' 011 = 500 kHz
' 100 = 1 MHz
' 101 = 2 MHz
' 110 = 4 MHz
' 111 = 8 MHz

OSCCON = %01010010 ' 2MHz
'DEFINE OSC 2 ' this line causes problems
LED1 var PortB.0
TRISB=%11111110

LOOP:
TOGGLE LED1
PAUSE 1000
WHILE OSCCON.2=0: WEND

GOTO LOOP


<b>My ultimate goal is to have a slow HPWM (around 1.7kHz) running at a slow clock speed.</b> Is this the right way to do it?
--------
Cheers
Squib

[mister_e]

It's just because 2MHZ is not supported by PBP.

to have a PAUSE 1000 @ 2MHZ you need to DEFINE OSC 4 and a PAUSE 500. Same for HPWM, to have 1.7KHZ @ 2MHZ multiply your frequency by two @4MHZ.

At 32...KHZ... from what i feel, you'll need to set the register manually and i can't tell if it's going to work. Just use the formula in the datasheet.