WORD bug

to all,

use of word in a for/next statement.

Code:

---


        init:
                decideInterval                var                WORD
                TIMEINTERVAL                con                600
        main:
                IF decideInterval = TIMEINTERVAL then
                        decideInterval = 0
                        (any code methods)
                ENDIF
                GOTO        MAIN
       
                END

---

It satisfies the IF condition unexpectedly. Changing the decideInterval type to BYTE and of course TIMEINTERVAL to max 255(or any 8Bit arbitrary value) will work correctly. Im using a PIC16F628 running 8MHz crystal oscillator. any ideas on this? thanks very much

regards,
yettie

This is no BUG. Uninitialized variables will contain random values.
Try assigning a value to your word variable, and then see how it works.

Code:

---

init:
        decideInterval var WORD
        TIMEINTERVAL con 600

main:
        IF decideInterval = TIMEINTERVAL then
          decideInterval = 0
          HIGH 0  ' LED on  RB0 ----|>|---/\/\/----gnd
        ELSE
          decideInterval = 600
          LOW 0  ' LED off
        ENDIF
        pause 500
        GOTO  MAIN

        END

---

If your LED blinks on/off, it's working properly.

dear bruce,

i failed to initialized the WORD but in my program. also my bad, this is my code.

Code:

---

        init:
                decideInterval                var                WORD
                TIMEINTERVAL                con                600
                decideInterval = 0

        main:
                decideInterval = decideInterval + 1
                IF decideInterval = TIMEINTERVAL then
                        decideInterval = 0                          ;resets the decideInteval
                        (a command output to LCD display)
                ELSE
                ENDIF
                GOTO        MAIN
       
                END

---

i verified it that it enters the IF/THEN statement with the decideInterval = 11 or other pseudo-randomly values. sorry for the incomplete info a while ago. but this post seems to be complete now.

thanks

regards,
yettie

Sorry, but I still do not understand why you think this is a bug?

With the PIC operating at 8MHz, you have an execution speed of 2 million single cycle instructions per second. That's fast..!

If you increment decideInterval on each pass through your loop, of course it will = 600 at some point. And very quickly.

Here's another example;

Code:

---

init:
      decideInterval  var  WORD
      TIMEINTERVAL          con  600
      decideInterval = 0

main:
      decideInterval = decideInterval + 1
      IF decideInterval = TIMEINTERVAL then
          decideInterval = 0
          GOTO Match
      ENDIF
      GOTO  MAIN

Match: ' End up here in approximately 11.4mS
      GOTO Match
       
                END

---

From Main, through the loop once, then back to Main at 8MHz only takes around 19uS. Now take 19uS * 600 for ~11.4mS.

It takes only ~11.4mS before you increment decideInterval from 0 to 600, and then the IF/THEN statement evaluates as TRUE, and program flow jumps to Match.

Note: I verified this (PBP v2.46). It does not jump to match at 11. Only once
decideInterval = 600.

bruce,

to make things clear. i've written it in a program to have a 31.25ms timer at a prescale of 1:8,yielding a 250ms to overflow TIMER1. i verified it in a oscilloscope that it is accurate.

Code:

---

define  debug_reg            porta                'nevermind my serial LCD display debugger
define  debug_bit          0
define  debug_baud          2400
define  debug_mode          1

define  inthand            checkNow
 
define OSC 8
CMCON=7

time        var        word
timeL        var        time.byte0
timeH        var        time.byte1
decideTimeInterval        var        word
TIMEINTERVAL            con      600

;-----------------------
setup:
  debug  12,"Starting",10,13,"  Program",4
  pause  2000
 
  intcon  = %11000000  ;setting up gie and peie bits
  time    = 3036                  ;calibrated to have 31.25ms scale
  tmr1L  = timeL                ;65536 - time (preload value)
  tmr1H  = timeH

  flag            = 0
 
  PIR1.0  = 0
  PIE1.0  = 1

  T1CON  = %110001    ;setting up to 1:8 prescale
                                  ;31.25ms x 8 = 250ms/count
;--------------------------------
main:
  if flag = 4 then                ;(250ms x 4 = 1s) second ticker
    flag = 0
    decideTimeInterval = decideTimeInterval + 1
    gosub  updateTime
  endif

  if decideTimeInterval = TIMEINTERVAL then                ;this one is the notorious routine. it's just a reset condition.
    decideTimeInterval = 0                                ;It resets unexpectedly.  In contrast to this,
  endif                                                        ;changing the decideTimeInterval to BYTE and of course
                                                        ;TIMEINTERVAL <= 255 will function properly


  goto main
;----------------------------
updateTime:
  DEBUG "Time:",#decideTimeInterVal
  return
     


;------------------------
;interrupt handler   
@checkNow           
  pie1.0  = 0
  flag    = flag + 1
  time    = 3036
  toggle = portb.3                ;my monitor to oscilloscope, it accurately toggles at 250ms cycle
  TMR1L  = timeL
  TMR1H  = timeH
  PIR1.0  = 0
  PIE1.0  = 1
  resume

---

i hope now that everything clear for you now. the decideTimeInterval counter now increments every second avoiding fast incrementing, like you said.

any ideas?

thanks and I appreciate very much

regards,
yettie

Hi Yettie,

I couldn't get your code to compile without errors. Try this;

Code:

---

@ DEVICE MCLR_OFF,LVP_OFF,HS_OSC,WDT_OFF
DEFINE  OSC 8
define  debug_reg            porta                'nevermind my serial LCD display debugger
define  debug_bit          0
define  debug_baud          2400
define  debug_mode          1

define  inthand            checkNow
 
CMCON=7
TRISB.3=0

'Variables for saving state in interrupt handler
wsave                  VAR        BYTE $70 system                ' Saves W
ssave                  VAR        BYTE bank0 system        ' Saves STATUS
psave                  VAR        BYTE bank0 system        ' Saves PCLATH
fsave                  VAR        BYTE bank0 system        ' Saves FSR
time                  var        word
flag              var  byte
decideTimeInterval var        word
TIMEINTERVAL      con  600

;-----------------------
setup:
  debug  12,"Starting",10,13,"  Program",4
  pause  2000
 
  intcon  = %11000000  ;setting up gie and peie bits
  time    = 3036                  ;calibrated to have 31.25ms scale
  tmr1H  = time.highbyte
  tmr1L  = time.lowbyte          ;65536 - time (preload value)
  flag    = 0
  decideTimeInterval = 0
  PIR1.0  = 0
  PIE1.0  = 1

  T1CON  = %00110001    ;setting up to 1:8 prescale
                                  ;31.25ms x 8 = 250ms/count
;--------------------------------
main:
  if flag = 4 then                ;(250ms x 4 = 1s) second ticker
    flag = 0
    decideTimeInterval = decideTimeInterval + 1
    gosub  updateTime
  endif

  if decideTimeInterval = TIMEINTERVAL then                ;this one is the notorious routine. it's just a reset condition.
    decideTimeInterval = 0                                ;It resets unexpectedly.  In contrast to this,
  endif                                                        ;changing the decideTimeInterval to BYTE and of course
                                                        ;TIMEINTERVAL <= 255 will function properly
  goto main
;----------------------------
updateTime:
  DEBUG "Time:",#decideTimeInterVal
  return
;------------------------
;interrupt handler
asm
checkNow
    ; Save FSR, PCLATH, STATUS and W registers
    movwf        wsave          ; Save W
    swapf        STATUS, W  ; Swap STATUS to W (swap avoids changing STATUS)
    clrf        STATUS            ; Clear STATUS
    movwf        ssave            ; Save swapped STATUS
    movf        PCLATH, W  ; Move PCLATH to W
    movwf psave            ; Save PCLATH
       
        ; isr routine
    bsf STATUS,RP0  ; bank 1
    bcf PIE1,0
    bcf STATUS,RP0  ; bank 0
    incf _flag,f    ; increment flag
    movlw 0x8
    xorwf PORTB,f  ; toggle portb.3
    movf _time,W
    movwf TMR1L
    movf _time+1,W
    movwf TMR1H
    bcf PIR1,0
    bsf STATUS,RP0  ; bank 1
    bsf PIE1,0
    bcf STATUS,RP0  ; bank 0
   
    ; Restore FSR, PCLATH, STATUS and W registers
    movf        fsave, W      ; retrieve FSR value
    movwf        FSR            ; Restore it to FSR
    movf        psave, W            ; Retrieve PCLATH value
    movwf        PCLATH            ; Restore it to PCLATH
    swapf        ssave, W            ; Retrieve the swapped STATUS value (swap to avoid changing STATUS)
    movwf        STATUS            ; Restore it to STATUS
    swapf        wsave, F            ; Swap the stored W value
    swapf        wsave, W    ; Restore it to W (swap to avoid changing STATUS)
    retfie                    ; Return from the interrupt   
endasm     

    end

---

Look in the manual, and at some of the MeLabs examples for assembler interrupts to find out why it works.

Hi Bruce

the code is actually working to my circuit. it's just that there might have some differences in our compilers. i'm compiling it in PBP with IDE of microcode. just to study the (bug?), i'm changing the "time" variable to WORD or BYTE modifier. using the WORD seems to be not working properly other than the byte. i already prototyped this program and testing it further. I will share you further info of what more I can find out. thanks!

Regards,
Yettie