PIC12F1822 program counter jumping around during debug and release programming

Question

I am having the most awful trouble getting things up and running with my PIC12F1822.

I'm using MPLAB 8.86, an ICD3 and have the chip, in a DIP package set up in a breadboard on my desk. As far as I can see, the connections are all reliable and okay. Things were working okay until yesterday evening and I've not moved/touched anything.

The schematic looks like this:

Test circuit design

Before I write any code which does any input based on switches or gets data from serial, I just want to twiddle some LEDs so I know everything is working.

Here's my code :

 list p=12F1822 ; list directive to define processor 
 #include <p12F1822.inc> ; processor specific variable definitions 
 __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF 
 __CONFIG _CONFIG2, _WRT_OFF & _PLLEN_OFF & _STVREN_OFF & _BORV_19 & _LVP_OFF 
 #DEFINE LED1 PORTA,.2 ;Status LED connected to Port A bit 1 
 D1 EQU 0x7D ;temp register, used during delay 
 D2 EQU 0x7E ;temp register, used during delay 
 D3 EQU 0x7F 
 ORG 0x0000 ; processor reset vector 
 GOTO START 
 ;----------------------------------------------------------------------------; 
 ;DELAY ROUTINE, FORCES THE PIC TO WASTE TIME FOR 0.1Seconds AT 16MHz; 
 DELAY 
 MOVLW 0X35 
 MOVWF D1 
 MOVLW 0XE0 
 MOVWF D2 
 MOVLW 0X01 
 MOVWF D3 
 DELAY_0 
 DECFSZ D1, F 
 GOTO $+2 
 DECFSZ D2, F 
 GOTO $+2 
 DECFSZ D3, F 
 GOTO DELAY_0 
 ;4 CYCLES 
 GOTO $+1 
 GOTO $+1 
 ;4 CYCLES (INCLUDING CALL) 
 RETURN 
 ;------------------------------------------ 
 START 
 ;DEVICE CONFIG STUFF 
 BANKSEL TRISA 
 MOVLW B'00000000' ;EVERYTHING ELSE IS OUTPUT 
 MOVWF TRISA 
 BANKSEL OSCCON 
 MOVLW B'01111010' ;PLL DISABLED, 16MHZ CLOCK SPEED, INTERNAL CLOCK 
 MOVWF OSCCON 
 BANKSEL ANSELA 
 CLRF ANSELA ;ALL PINS AS DIGITAL 
 BANKSEL ADCON1 
 MOVLW B'00001111' 
 MOVWF ADCON1 ;ALSO TURNS OFF ANALOG THINGS 
 BANKSEL CM1CON0 CLRF CM1CON0 ;ALL COMPARATORS OFF 
 BANKSEL PORTA 
 CLRF PORTA ;CLEAR EVERYTHING ON PORT A BEFORE WE START, EXIT WITH BANK0 SELECTED 
 LOOP 
 ;BLINK THAT LED LIKE YOUR LIFE DEPENDED ON IT 
 BCF LED1 
 CALL DELAY 
 BSF LED1 
 CALL DELAY 
 GOTO LOOP 
 END 

Nothing too exciting.

When I make this and then program it in in release mode I just get one LED stuck on.

When I make this in debug mode and then try to step through with the debugger/ICD3/MPLAB - I can't reliably get the code to run.

Specifically, the program counter seems to be jumping around all over the place.

To my understanding, when you reset the MCU using the yellow button in MPLAB, the program should go to the top and then wait for you to either run or step through - like this:

One

The location of the PC is indicated by the green arrow - mine keeps showing up in places which are not the start! It shows up in all manner of places e.g.

Two

This makes debugging a pain - and - indicates that something is really wrong.

I have no idea what - has anyone else come across anything like this?

It isn't limited to this code snippet either. In [This Example] after a reset the PC jumps in at BANKSEL OSCCON (line 138) and when running seems get get stuck inside AUXHELLOWORLD (i.e. the LED keeps flashing forever).

Any insight you might have would be most appreciated Best D

• Rocketmagnet: Have you tried removing the resistor and LED attached to PGC ?
• mynameisdev: yes, to no avail

Answer 1

I used an assembly template located here from Bill Howl on this website and wrapped your delay routine around it.

I payed particular attention to the port initialization routine example given on the microchip datasheet pg 124 Example 12-1 Initializing port A. The BANKSEL PORTA just before the delay routine and port toggling kicks off is crucial! Doesn't appear to have the problem your are experiencing with the program counter. Simulated for 806 seconds... And no issues. Sometimes it helps to clean the project code up by clicking project, clean.

Give this source code a try

Your second piece of code is causing stack overflow errors
CORE-E0001: Stack over flow error occurred from instruction at 0x000037
CORE-E0001: Stack over flow error occurred from instruction at 0x000037
CORE-E0001: Stack over flow error occurred from instruction at 0x000037
CORE-E0001: Stack over flow error occurred from instruction at 0x000038

This is because you are missing the return statement in the AUXHELLOWORLD block. enter image description here
When your code starts it would cause an infinite never-ending loop of these two calls (initialise and auxhelloworld) each time adding to the stack and never getting popped back. Eventually the stack will be overwhelmed and lose track of where it is supposed to return causing strange code behaviour and program counter to jump about.

START
CALL INITIALISE
CALL AUXHELLOWORLD

Try the template! Really you should learn c code and download the microchip or Hitech c compiler. It will make your life much easier... You won't go back to assembly!
Furthermore you can also incorporate assembly in c code, if you really needed the specialised code.

Answer 2

I was able to compile and simulate this code without issues in MPLAB v8.84, with no program counter jumpiness, in both debug and release mode. I can see the port A bit toggling just fine with MPLAB sim.

Did you try toggling LATA instead of PORTA?

Did you specify MPASM to build absolute code?

Answer 3

This program for the 12F1822 which also flashes an LED connected to RA2 works OK on a PCB of mine:

;flasher.asm
;simple program for PIC12F1822 to flash LED on RA2 (pin 5)
 list p=12f1822 ;list directive to define processor
 #include "p12f1822.inc" ;processor specific variable definitions
 errorlevel -302
 __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _BOREN_OFF
 __CONFIG _CONFIG2, _LVP_OFF & _PLLEN_ON
;-----------------------------------------------------------------
;defines
;-----------------------------------------------------------------
 #define LED LATA2 ; (pin 5)
;-----------------------------------------------------------------
;variables
;-----------------------------------------------------------------
 cblock 0x70 ;same bank as LATA
 Counter1
 Counter2
 endc
;------------------------------------------------------------------
;initialisation
;------------------------------------------------------------------
 org 0
 banksel OSCCON
 movlw b'01110000' ;HFINTOSC (32 MHz with PLL enabled)
 movwf OSCCON
 banksel OSCSTAT
 btfss OSCSTAT,HFIOFR ;HFINTOSC ready?
 goto $-1
 btfss OSCSTAT,PLLR ;PLL ready?
 goto $-1
 banksel TRISA 
 bcf TRISA,LED ;LED output
 banksel LATA
;-----------------------------------------------------------------------
;main program loop
;-----------------------------------------------------------------------
loop:
 bsf LATA,LED ;LED off
 call dly
 bcf LATA,LED ;LED on
 call dly
 goto loop
dly:
 movlw 0xFF
 movwf Counter1
dly1:
 movlw 0xFF
 movwf Counter2
dly2:
 decfsz Counter2,F
 goto dly2
 decfsz Counter1,F
 goto dly1
 return 
 end