16F688 wake with comparators and internal Vref

I have a piezo disc w 1Meg in parallel to RC0 of 16F866. Working fine to detect vibration when configured as analog, using ADCIN.
Now I want to wake the PIC from sleep when vibration is detected, when voltage on PORTC.0 exceeds, say, 0.2v (lowest available setting) using internal Vref. I'm using comparator 2, mode 010 with CIS and C2INV bits set. It sleeps, but never wakes.

What am I missing? Relevant code:

Code:

OSCCON=%01100001 '4 mhz clock default DEFINE OSC 4 'for sLCD can change later DEFINE ADC_BITS 8 DEFINE ADC_SAMPLEUS 50 DEFINE ADC_CLOCK 3 VRCON=0 'volt ref off ANSEL=%00010000 'piezo input analog on AN4 RC0 CMCON0=0 'comparators off, pins analog=0 (off/digital=7) INTCON=0 'interrupts disabled ' ------------ pins piezo VAR PORTC.0 LED VAR PORTA.2 option_reg.7=0 'WPU ports A only 'WPUA =%00000000 'PUSHBUTTONS on port A later TRISA=%00000000 ' TRISC=%00000001 'analog ch4 RC0 piezo PORTA=0 : PORTC=0 '-------------- variables i var byte temp var BYTE piezo_analog var byte version CON 205 CLEAR '-------------- code LED=1 'startup, power on read 0, temp if temp<>version then write 0, version 'save version to EEPROM 0 pause 1000 'show power on LED LED=0 CMCON0=%00101010 ' VRCON=%10100001 'approx 0.2 volt Vref PAUSEUS 10 'allow Vref to settle INTCON.6=1 'PEIE for wake PIR1.4=0 'clear flag 'TRIS 'for lowest sleep power, later @ sleep @ nop wake: 'v205 sleeps but not waking CMCON0=0 'comparators off now PIR1.4=0 'clear LED=1 'show awake END