Code running 19 times slower than intended

[jellis00]

I have taken the attached code from a development board (EASYPIC6) to a prototype board and it is running 38 times slower in the prototype board than the development board. The prototype uses the same code, the same MCU (18F4550) and the same XTAL (8 MHz) so don't understand why it would run 38 times slower. How do I know it is 38 times slower?...I have some blinking LEDs at the beginning of each routine for test purposes and a heartbeat LED in the main loop that are coded to be on for only 0.5 secs (which they do in the development board), but they are on for 19 secs in the prototype. Hence 19/0.5 = 38 times slower.

Can anyone look at this code and give me any ideas why this code would run 38 times slower in the prototype? I checked to make sure the 18F2550.inc file had the configs commented out, since they are set by this code.

Post Note: Adding the code made this posting exceed the 10,000 characer limit. I will try to post the code in another posting.

[ScaleRobotics]

I seem to be missing the attachment.

[jellis00]

I will try to post the code in another posting.

  
Pause 10     ' This statement is placed at beginning of code for ICD use

'Configuration Fuses
    ASM ; 18F2550/4550, 8mhz crystal
       __CONFIG   _CONFIG1L, _PLLDIV_2_1L & _CPUDIV_OSC4_PLL6_1L & _USBDIV_2_1L
       __CONFIG   _CONFIG1H, _FOSC_HSPLL_HS_1H
       __CONFIG   _CONFIG2L, _PWRT_ON_2L & _BOR_OFF_2L & _VREGEN_ON_2L
       __CONFIG   _CONFIG2H, _WDT_OFF_2H & _WDTPS_512_2H
       __CONFIG   _CONFIG3H, _PBADEN_OFF_3H ; PortB resets as digital
       __CONFIG   _CONFIG4L, _LVP_OFF_4L & _XINST_OFF_4L
    ENDASM

' Define Hardware / Set Registers     
    DEFINE OSC 16
    DEFINE I2C_SLOW 1   ' Set i2c to the standard speed
    DEFINE I2C_HOLD 1   ' Enable recieving i2c device to pause communication
    Include "Modedefs.Bas"  
    INCLUDE "ALLDIGITAL.pbp"  
    INCLUDE "DT_INTS-18.bas"    
    INCLUDE "ReEnterPBP-18.bas"

    TRISA = 0           ' PortA output connections used for LCD interface
    TRISB = %00001100   ' RB2 & RB3 set as RTC Alarm1 & Alarm2 inputs 
                        ' PORTB.2 is an input from switch grounding
                        ' PORTB.4 is used during test as a Green LED heartbeat
                        ' and as a USB connected indicator during ops 
    TRISC.1 = 0         ' PORTC.1 used during test as a RED LED output
    TRISC.2 = 0         ' PortC.2 is used for the LCD R/W connection
    
'Declare Variables, Aliases & Constants 
    day_cnt  VAR BYTE      ' Counter for day number during monthly epoch
    ext_pwr  VAR PORTC.0   ' Alias to control power to Ultrasonic sensors
    i        VAR Byte      ' Index in FOR-NEXT loops
    J        VAR BYTE      ' Index to EEPROM address for avg. range store
    LED_RED  VAr PortC.1   ' Red LED used to indicate battery is low
    LED_GRN  VAR PortB.4   ' Green LED used to indicate USB connected
    rng0     VAR w0.Byte0  ' LSB of range measurement when right justified
    rng1     VAR w0.byte1  ' MSB of range measurement when right justified 
    SCL      VAR PORTB.1   ' I2C clock pin 
    SDA      VAR PORTB.0   ' I2C data pin
    Spare_1  VAR PORTB.7   ' PGD for ICSP & Spare I/O for normal ops
    Spare_2  VAR PORTB.6   ' PGC for ICSP & Spare I/O for normal ops
    w0       var word      ' W0 is the word value of the range data 
               
' Constants
    RTCdevice CON $D0  ' Device write address = %11010000 for RTC
    srfdevice CON $E0  ' Device address for SRF02 ultrasonic RangeFinder
    Vthr      CON 46   ' Threshold (3.3v) triggers battery low voltage
                    
'SETUP FOR USING DS1337 Real Time Clock
         
'Initialize LEDs to off
    LOW LED_GRN
    LOW LED_RED
GOSUB InitializeDisplay  ' Initialize LCD before starting mainloop
GOSUB SetTimeAndDate     ' Set RTC time/date before starting mainloop  
        
' START SUBROUTINES
GOTO JumpPoint ' Jump over all subroutines

InitializeDisplay:
     ' Blink LED_GRN twice to indicate entered IntializeDisplay
           For i = 0 to 1
               HIGH LED_GRN
               Pause 500
               LOW LED_GRN
               PAUSE 500
           Next
     ' Saving characters by eliminating in post
Return

SetTimeAndDate:  ' Subroutine to set current time, date and alarm  

    ' Blink LED_GRN 3X times to indicate entered SetTimeAndDate
           For i = 0 to 2
               HIGH LED_GRN
               Pause 500
               LOW LED_GRN
               PAUSE 500
           Next
      ' Saving characters by eliminating in post 
Return
'  END OF SUBROUTINES 
            
JumpPoint:

'Initialize epoch indexes on powerup/reset
    day_cnt = 0
    WRITE 9, day_cnt     ' Store new epoch initialized day_count
    Pause 20
    J = 0                ' Initialize index at EEPROM start address 
    WRITE 10,J           ' Store new epoch initialized J index
    Pause 20

' SETUP FOR INTERRUPTS  
ASM
INT_LIST  macro    ; IntSource,         Label,  Type, ResetFlag?
        ;INT_Handler   USB_Handler
        INT_Handler   INT2_INT,        _Range,   PBP,  yes
    endm
    INT_CREATE                ; Creates the interrupt processor
ENDASM

' Per DT, DT_INTS already takes care of setting INTCON and RCON registers
' but this doesn't work unles INTCON2 set per below:
    INTCON2 = %10000000  ' Set INT2 for falling edge (Bit4-low)
                         ' on RTC's interrupt.
                         ' Disable all PortB pull-ups (Bit7-high)
    RTC_INT_FLG  VAR INTCON3.1 'INT2 interrupt flag from RTC..DT_INTS handles

@    INT_ENABLE   INT2_INT     ; enable external (INT) interrupts
LOW ext_pwr  ' Turn off power to SRF02 until I2C bus is needed again        

' Begin Main Program Loop
mainloop:
    PAUSE 100 ' Without this Pause, there's nothing to keep the WDT clear.
              ' HIGH, LOW & GOTO don't generate CLRWDT instuctions.
    HIGH LED_GRN     ' Blink LED_GRN during main loop
    
    ' Place code here to put MCU and Ultrasonic Ranger in SLEEP mode.
    ' while waiting for clock interrupt to wakeup from SLEEP mode.
    
    ' Awaiting interrupt from RTC
    
    PAUSE 1000
    LOW LED_GRN  ' Turn off LED_GRN as Heartbeat during mainloop
    Pause 900

Goto mainloop   ' Do it forever     

' Begin Interrupt Handler 
Range:
     ' Saving characters by eliminating in post
    ' Blink LED_RED 3X to indicate entered Range ISR
           For i = 0 to 2
               HIGH LED_RED
               Pause 500
               LOW LED_RED
               PAUSE 500
           Next
@ INT_RETURN

'End of Interrupt Handler

[mackrackit]

If you are using the same code and the same PIC® it has to be a hardware problem.

Check to OSC to make sure it is OK. Maybe wrong/bad capacitor??

[jellis00]

If you are using the same code and the same PIC® it has to be a hardware problem.

Check to OSC to make sure it is OK. Maybe wrong/bad capacitor??

Thanks for this tip! I put an Oscilloscope on to Pin 9 (OSC1) of the 18F2550MCU and it appears that the crystal is not oscillating. Can't figure out why not.
I am using an 8 MHz crystal from Abracom (their P/n ABL-8-B2) with two 27 pf capacitors as C1 and C1. This crystal specs a CL of 18 pf. By my calculation I am close to that if you assume a PCB stray capacitance of Cs=4 pf (my terminatons to crystal and capacitors from the MCU are very short on the PCB), the calculation goes like this:
CL = Cs +(c1 X c2)/(c1+c2). When usining C1=C2=27pf in this calculation CL comes out to 17.5 pf which is very close to the spec'd 18 pf and I can't believe this difference would prevent the OSC from working.
I am operating the MCU with a regulated supply voltage of 3.1 volts, so the drive on the crystal should be sufficient to cause oscillation.
One thing I really don't understand is why the MCU is still operating (granted at 38 times slower than expected) when the OSC is not even oscillating.
Can anyone give me some hints or advice how to resolve this??

[mackrackit]

I can not help much on the crystal as I do not use them. For good or bad I use those three pin resonators, that way I do not have to mess with capacitors.

I would guess the chip has defaulted to 31 kHz, that is what it is running at.

You could use the internal OSC. This chip has an 8 MHz built in. May or may not be good enough for serial...

[jellis00]

I finally found the problem thanks to rteo who advised that the 18F2550/4550 data sheet shows in one place that the external osc won't function with a supply voltage to the MCU of less than 4.2 volts. I had been running a supply voltage of 3.3 volts as a battery power conservation measure. I then experimented and discovered, rteo is partially correct.....my 18F2550 external osc circuit won't oscillate reliably until the supply voltage is at least 3.6 volts.
This discovery is going to make me change the design for this product to a 4.2 volt supply rail.