16F1824 "HPWM 2" woes (command seemingly forces PortC.3 from analogue to digital)

[HankMcSpank]

I have a 16F1824 PortC.3 (ie pin 9) set as an analogue ADC input pin...it works fine, until my program code gets reaches this line...

HPWM 2, duty, 32767

(where duty is a variable representing erhm...the duty cycle)

once that point is reached, my PortC.3 apparently flips to a digital pin....ie when I vary my analogue input signal into PortC.3, I observe only a '0' or a '1' as the incoming Signal level.

If I use the following as a workaround on each occurence...

HPWM 2, duty, 32767
TRISC =  %11110111     ' PIN 7 RC3 HPWM  OUTPUT

...then all is well again (my ADC readings are as expected....ie between 0 & 255)

Now I've never used the 2nd channel of PWM before (ie I've always just used one channel...."HPWM 1, duty, 32767"), so it's likely something simple I'm doing wrong, but I've looked at this so long now that the number of the beast starts appearing in my main loop. (which probably means it's time to get a fresh pair of eyes on the case)

Any ideas?

Here's the full test code...

REDRUM, REDRUM,REDRUM,REDRUM,REDRUM, REDRUM,REDRUM,REDRUM,REDRUM, REDRUM,REDRUM,REDRUMREDRUM, REDRUM,REDRUM,REDRUM

@ __CONFIG _CONFIG1, _FCMEN_OFF & _FOSC_INTOSC & _WDTE_OFF & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOREN_OFF & _PWRTE_OFF & _LVP_OFF
@ __CONFIG _CONFIG2, _LVP_OFF

DEFINE  OSC 4   

Osccon = %01101010   'sets the internal oscillator to 4Mhz

DEFINE DEBUG_BAUD 9600
DEFINE DEBUG_MODE 2
DEFINE DEBUG_REG PORTC
DEFINE DEBUG_BIT 4

DEFINE ADC_BITS  8     ' ADCIN resolution  (Bits)
DEFINE ADC_CLOCK 1     ' ADC clock source  (Fosc/8)
DEFINE ADC_SAMPLEUS 11 ' ADC sampling time (uSec)

ADCON0 = %00010101    'AN5 (Pin 9) Enabled for BACKGROUND adc'ING VIA SPECIAL EVENT TRIGGER  + ADC On
ADCON1 = %01000011     'set ADC +ve ref to be the internal Fixed VREF   
FVRCON = %11000010     'turn fixed voltage reference on & set it to 2.048V (last two bits set the voltage ...01 =1.024V,10=2.048


CM1CON0 = 0   ' COMPARATORS OFF
CM1CON1 =0
CM2CON0 = 0   ' COMPARATORS OFF
CM2CON1 =0    
CPSCON0 = 0   'CAPACTIVE SENSE MODULE OFF
RCSTA.7 = 0   'SERIAL PORT OFF

TRISA =  %11111111
TRISC =  %11110111     ' PIN 7 RC3 HPWM  OUTPUT
ANSELA = 0
ANSELC = 0

CCP2CON    = %00001100    'NOT ENTIRELY CONFIDENT ABOUT THIS ONE!

Sig_In          VAR BYTE  ; a variable to store to DC level coming in on pin 19 (RA0)
duty            var word
latest_sample   var word


'setup the AtoD & special event register to capture samples in the background
T1CON = %00000001         ' timer1 on
CCP4CON = %0001011     'set CCP4 to special event trigger.

CCPR4H = 0         ' preset for timer1 match (MSB register)
CCPR4L = 250       '  @16Mhz, 200 gives 20,000khz sample & 250 gives 16khz sample.

duty = 255
HPWM 2, duty, 32767
TRISC =  %11110111     ' PIN 7 RC3 HPWM  OUTPUT

TEST: 
latest_sample = ADRESH
PAUSE 500
debug dec LATEST_SAMPLE,13,10
GOTO TEST