Strange question.
I have two PICDEM FS USB Demo Boards from Microchip (with the PIC18F45K50 chip on them). I ordered a second one because the first was acting really strange and I figured it was defective. But the second one does it too.
The behavior is that it seems like the clock on the chip only runs when I touch the OSC1 pin as though my body is somehow acting as the ground for the chip. I have a male-to-male header wire stuck in the OSC1 header port and when I pinch it, the LEDs blink as though the system clock is running.
If I take my fingers off, it's like the system clock stops. I have a few different programs that flash based on time, pressing the buttons, or turning the potentiometer. But they all have the same behavior: unless I pinch the wire, nothing happens, like the system clock is stopped. Note that connecting the OSC1 pin to the GND pin does accomplish the same thing, so my hypothesis about my body acting as the ground doesn't seem to make much sense.
I can't find anything about this in the user guide for the board, or any help threads mentioning the same behavior.
My only guess is that maybe it's something about the configuration flags I'm using in my programs, but from what I understand they look fine:
// PIC18F45K50 Configuration Bit Settings
// CONFIG1L
#pragma config PLLSEL = PLL4X // PLL Selection (4x clock multiplier)
#pragma config CFGPLLEN = OFF // PLL Enable Configuration bit (PLL Disabled (firmware controlled))
#pragma config CPUDIV = NOCLKDIV// CPU System Clock Postscaler (CPU uses system clock (no divide))
#pragma config LS48MHZ = SYS24X4// Low Speed USB mode with 48 MHz system clock (System clock at 24 MHz, USB clock divider is set to 4)
// CONFIG1H
#pragma config FOSC = HSH // Oscillator Selection (HS oscillator, high power 16MHz to 25MHz)
#pragma config PCLKEN = ON // Primary Oscillator Shutdown (Primary oscillator enabled)
#pragma config FCMEN = OFF // Fail-Safe Clock Monitor (Fail-Safe Clock Monitor disabled)
#pragma config IESO = OFF // Internal/External Oscillator Switchover (Oscillator Switchover mode disabled)
// CONFIG2L
#pragma config nPWRTEN = ON // Power-up Timer Enable (Power up timer enabled)
#pragma config BOREN = SBORDIS // Brown-out Reset Enable (BOR enabled in hardware (SBOREN is ignored))
#pragma config BORV = 190 // Brown-out Reset Voltage (BOR set to 1.9V nominal)
#pragma config nLPBOR = OFF // Low-Power Brown-out Reset (Low-Power Brown-out Reset disabled)
// CONFIG2H
#pragma config WDTEN = OFF // Watchdog Timer Enable bits (WDT disabled in hardware (SWDTEN ignored))
#pragma config WDTPS = 32768 // Watchdog Timer Postscaler (1:32768)
// CONFIG3H
#pragma config CCP2MX = RC1 // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF // PORTB A/D Enable bit (PORTB<5:0> pins are configured as digital I/O on Reset)
#pragma config T3CMX = RC0 // Timer3 Clock Input MUX bit (T3CKI function is on RC0)
#pragma config SDOMX = RB3 // SDO Output MUX bit (SDO function is on RB3)
#pragma config MCLRE = ON // Master Clear Reset Pin Enable (MCLR pin enabled; RE3 input disabled)
// CONFIG4L
#pragma config STVREN = ON // Stack Full/Underflow Reset (Stack full/underflow will cause Reset)
#pragma config LVP = ON // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled if MCLRE is also 1)
#pragma config ICPRT = OFF // Dedicated In-Circuit Debug/Programming Port Enable (ICPORT disabled)
#pragma config XINST = OFF // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled)
// CONFIG5L
#pragma config CP0 = OFF // Block 0 Code Protect (Block 0 is not code-protected)
#pragma config CP1 = OFF // Block 1 Code Protect (Block 1 is not code-protected)
#pragma config CP2 = OFF // Block 2 Code Protect (Block 2 is not code-protected)
#pragma config CP3 = OFF // Block 3 Code Protect (Block 3 is not code-protected)
// CONFIG5H
#pragma config CPB = OFF // Boot Block Code Protect (Boot block is not code-protected)
#pragma config CPD = OFF // Data EEPROM Code Protect (Data EEPROM is not code-protected)
// CONFIG6L
#pragma config WRT0 = OFF // Block 0 Write Protect (Block 0 (0800-1FFFh) is not write-protected)
#pragma config WRT1 = OFF // Block 1 Write Protect (Block 1 (2000-3FFFh) is not write-protected)
#pragma config WRT2 = OFF // Block 2 Write Protect (Block 2 (04000-5FFFh) is not write-protected)
#pragma config WRT3 = OFF // Block 3 Write Protect (Block 3 (06000-7FFFh) is not write-protected)
// CONFIG6H
#pragma config WRTC = OFF // Configuration Registers Write Protect (Configuration registers (300000-3000FFh) are not write-protected)
#pragma config WRTB = OFF // Boot Block Write Protect (Boot block (0000-7FFh) is not write-protected)
#pragma config WRTD = OFF // Data EEPROM Write Protect (Data EEPROM is not write-protected)
// CONFIG7L
#pragma config EBTR0 = OFF // Block 0 Table Read Protect (Block 0 is not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF // Block 1 Table Read Protect (Block 1 is not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF // Block 2 Table Read Protect (Block 2 is not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF // Block 3 Table Read Protect (Block 3 is not protected from table reads executed in other blocks)
// CONFIG7H
#pragma config EBTRB = OFF // Boot Block Table Read Protect (Boot block is not protected from table reads executed in other blocks)
Any help would be appreciated.
It turned out to be just as I suspected, one of the configuration flags was wrong. Changing the setting of FOSC fixed the problem. The new line is:
#pragma config FOSC = INTOSCIO // Oscillator Selection (Internal oscillator)
Being new to PIC programming I'm not sure what the external oscillator was that it was expecting but somehow it ended up being me.