I hate outsmarting myself. I intentionally replaced that RETURN, argh...

I had also replaced the YES flag. I should have stepped away and taken a break, to take a different look at my code a few minutes later. I somehow thought more was going on and had to handle the flag myself, I obviously didn't. The interrupt won't take off again unless I call Start.

Code:
@   __CONFIG    _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
@   __CONFIG    _CONFIG1H, _FOSC_HSPLL_HS_1H
@   __CONFIG    _CONFIG2L, _PWRT_OFF_2L & _BOR_ON_2L & _BORV_1_2L & _VREGEN_ON_2L
@   __CONFIG    _CONFIG2H, _WDT_OFF_2H
@   __CONFIG    _CONFIG3H, _CCP2MX_ON_3H & _PBADEN_OFF_3H & _LPT1OSC_OFF_3H & _MCLRE_ON_3H
@   __CONFIG    _CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _ICPRT_OFF_4L & _XINST_OFF_4L

DEFINE OSC 48

ADCON1 = %00001111                      ' A/D CONTROL REGISTER 1
'   Bit 7-6 Unimplemented: Read as ‘0’
'   Bit 5   VCFG1: Voltage Reference Configuration bit (VREF- source)
'               0 = VSS
'               1 = Vref- (AN2)
'   Bit 4   VCFG0: Voltage Reference Configuration bit (VREF+ source)
'               0 = VSS
'               1 = Vref+ (AN3)
'   Bit 3-0 PCFG3:PCFG0: A/D Port Configuration Control bits:
'               1111 = All digital
'               1110 = All digital, AN0 analog
'               1101 = All digital, AN0 & AN1 analog

INTCON2 = %00000000                     ' INTERRUPT CONTROL REGISTER 2
'   Bit 7   RBPU: PORTB Pull-up Enable bit
'               1 = All PORTB pull-ups are disabled
'               0 = PORTB pull-ups are enabled provided that the pin is an input
'                   and the corresponding WPUB bit is set.
'   Bit 6   INTEDG0: External Interrupt 0 Edge Select bit
'               1 = Interrupt on rising edge
'               0 = Interrupt on falling edge
'   Bit 5   INTEDG1: External Interrupt 1 Edge Select bit
'               1 = Interrupt on rising edge
'               0 = Interrupt on falling edge
'   Bit 4   INTEDG2: External Interrupt 2 Edge Select bit
'               1 = Interrupt on rising edge
'               0 = Interrupt on falling edge
'   Bit 3   Unimplemented: Read as ‘0’
'   Bit 2   TMR0IP: TMR0 Overflow Interrupt Priority bit
'               1 = High priority
'               0 = Low priority
'   Bit 1   Unimplemented: Read as ‘0’
'   Bit 0   RBIP: RB Port Change Interrupt Priority bit
'               1 = High priority
'               0 = Low priority

T0CON = %10000011                       ' TIMER0 CONTROL REGISTER
'   Bit 7   TMR0ON: Timer0 On/Off Control bit
'               1 = Enables Timer0
'               0 = Stops Timer0
'   Bit 6   T08BIT: Timer0 8-Bit/16-Bit Control bit
'               1 = Timer0 is configured as an 8-bit timer/counter
'               0 = Timer0 is configured as a 16-bit timer/counter
'   Bit 5   T0CS: Timer0 Clock Source Select bit
'               1 = Transition on T0CKI pin
'               0 = Internal instruction cycle clock (CLKO)
'   Bit 4   T0SE: Timer0 Source Edge Select bit
'               1 = Increment on high-to-low transition on T0CKI pin
'               0 = Increment on low-to-high transition on T0CKI pin
'   Bit 3   PSA: Timer0 Prescaler Assignment bit
'               1 = Timer0 prescaler is NOT assigned. Timer0 clock input
'                   bypasses prescaler.
'               0 = Timer0 prescaler is assigned. Timer0 clock input comes from
'                   prescaler output.
'   Bit 2-0 T0PS2:T0PS0: Timer0 Prescaler Select bits
'               111 = 1:256 Prescale value
'               110 = 1:128 Prescale value
'               101 = 1:64 Prescale value
'               100 = 1:32 Prescale value
'               011 = 1:16 Prescale value
'               010 = 1:8 Prescale value
'               001 = 1:4 Prescale value
'               000 = 1:2 Prescale value

INCLUDE "DT_INTS-18.bas"            ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"         ' Include if using PBP interrupts

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR0_INT,  _EndTimer,    PBP,  yes
    endm
    INT_CREATE                      ; Creates the interrupt processor
ENDASM

    TRISA = %00000000
    TRISB = %11110000               '  Set columns to input, rows to output
    TRISC = %00000000
    TRISD = %00000000
    TRISE = %00000000

TimerLed    VAR PORTD.1

    LOW TimerLed
    GOTO Main

StartTimer:
    TMR0H = 109                     ' 50 mS Timer
    TMR0L = 144
    HIGH TimerLed             
@ INT_ENABLE  TMR0_INT              ; enable Timer 0 interrupts
RETURN

EndTimer:
    LOW TimerLed             
@ INT_RETURN

KeypadInput:
    PORTB = %00001110               ' Row 1
    IF PORTB.4 = 0 THEN             ' Column 1
        GOSUB StartTimer
        WHILE PORTB.4 = 0: WEND
    ENDIF
RETURN

Main:
    GOSUB KeypadInput               ' Scan 4 x 4 keypad
'       Future logic goes here.
    GOTO Main
END
Name: Timer0b.JPG Views: 313 Size: 93.9 KB

Eeesh, thanks guys! It works perfectly now.

Robert