I2c, srf02, 16f688 -> ultrasonic rangefinder

[RussMartin]

I'm noodling (finally) with an SRF02 ultrasonic rangefinder, communicating via I2C with a 16F688.

I've used a similar program for an IR rangefinder, but I can't get this to work.

Blinky tests: Done
SRF02 indicator: Flashes about once per second
Scope: Shows both SDA and SCL lines active about once per second
Ultrasonic output: The SRF02 is "pinging", tested with an ultrasonic receiver connected to the scope.

Everything external appears to work except getting the comparison done and/or the yellow LED to so indicate

I've tried several variations, always coming back to a straightforward adaptation of code posted by jellis00 some time ago (thread is archived).

Where have I gone wrong?

@ __config _INTOSCIO & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF & _BOD_OFF & _IESO_OFF & _FCMEN_OFF & _CP_OFF & _CPD_OFF

                                        '      INPUTS:
MODE    VAR PORTA.3                     ' MODE jumper; default is HIGH (MODE B)
                                        '      I2C INTERFACE:
SDA     VAR PORTA.5                     ' Serial data
SCL     VAR PORTA.4                     ' Serial clockS                 
                                        '      OUTPUTS:
RELAY   VAR PORTA.0                     ' Relay driver
GLED    VAR PORTC.1                     ' LED status indicator, green
YLED    VAR PORTC.2                     ' LED status indicator, yellow
                                        '      VARIABLES:
KLIX    VAR BYTE                        ' Generic counter variable
FAR     VAR BYTE                        ' Analog value, MAX setting, PORTA.1
NEAR    VAR BYTE                        ' Analog value, MIN setting, PORTA.2
RANGE0  VAR BYTE
RANGE1  VAR BYTE

DEFINE  ADC_BITS        8               ' Number of bits in ADC result
DEFINE  ADC_CLOCK       3               ' Set ADC clock source to RC
DEFINE  ADC_SAMPLEUS    25              ' Set ADC sampling time in microseconds

ANSEL =%00000110                        ' Enable ADC channels AN2-AN1
CMCON0=%00000111                        ' Disable the comparators
OSCCON=%01100000                        ' Configure oscillator 4MHz ($60)
TRISA =%00001110                        ' Set ports A3-A2-A1 as inputs
TRISC =%00000000                        ' Set all ports C as outputs

        RELAY=0 : KLIX=0                ' Set relay LOW and clear counter value
        GLED=0  : YLED=0                ' Set LEDs to OFF 
        
        IF MODE=0 THEN                  ' Wait 5 seconds to stabilize detector
            FOR KLIX=1 TO 5             ' During this time:
                GLED=1 : PAUSE 500      ' Show MODE A by flashing green
                GLED=0 : PAUSE 500
                NEXT KLIX               '  or
            ELSE                        
            FOR KLIX=1 TO 5             ' Show MODE B by flashing yellow
                YLED=1 : PAUSE 500
                YLED=0 : PAUSE 500              
                NEXT KLIX              
            ENDIF   
                                        
        GLED=1                          ' Set green LED ON for "Ready"
                                        '      DETECTOR
MAIN:   I2CWRITE SDA,SCL,$E0,0,[80]     ' Request range in inches
        PAUSE 100                       ' Wait for ranging to finish
        I2CREAD SDA,SCL,$E0,2,[RANGE1,RANGE0]   ' Read range
        ADCIN 2,FAR                     ' Get the maximum setting
        ADCIN 1,NEAR                    ' Get the minimum ("window") setting
        IF ( RANGE0 < FAR AND RANGE0 > NEAR ) THEN
            GLED=0 : YLED=1
            ELSE
            GLED=1 : YLED=0
            ENDIF
        PAUSE 1000
        GOTO MAIN 
            
        END