AVR-Chat

I'm having a problem getting an ADC reading, in a transient case.
I'm probably missing something obvious.. :-P


The processor has recently come out of reset, so I'm trying to assume nothing.
Ints are disabled, this is a test that I have to make before the main system comes up and the normal ADC routines would work, which are interrupt driven and free running.

The only discrepancy I see with the data sheet is that they call out the register as ADCSRA, but the M128def.inc file I have has no such callout, they used ADCSR.

I want to read a voltage on channel 2, with the internal 2.5V reference.

I set bit 2 of port F as input, by:

	lds	TEMP,DDRF	;There are other pins set that I don't want to bother
	andi	TEMP,0xFB	;Set bit 2 (ADC channel 2) to input
	sts	DDRF,TEMP 	;

Then I wait for any pending conversion to complete:

Volt_First:
	sbic	ADCSR,ADSC	;Loop here till ADSC is zero
	rjmp	Volt_First	;This makes sure any pending conversion finishes.


Then I set up to read channel 2

Volt_Test_Setup:
	ldi	TEMP,0xE2	;11XXXXXX Internal 2.5V Vref
				;XX1XXXXX Left adjust result into ADCH
	out	ADMUX,TEMP	;XXX00010 Select battery input channel

	ldi	TEMP,0x83	;1XXXXXXX Enable ADC
				;X0XXXXXX Don't Start Conversion yet
				;XX0XXXXX Don't freerun
				;XXX0XXXX Interrupt flag (not needed)
				;XXXX0XXX Int disabled
	out	ADCSR,TEMP	;XXXXX111 125 kHz clock from 16 MHz Xtal

	ldi	TEMP,0xFF	;
VT_Delay:
	dec	TEMP		;Delay,  before starting.
	brne	VT_Delay	;15uS.

	sbi	ADCSR,ADSC	;Start the ADC


So now, I wait till this conversion completes, discard it, and run another.


Volt_First_Wait:
	sbic	ADCSR,ADSC	;Atmel says to toss the first conversion result.
	rjmp	Volt_First_Wait	;So just wait till it's done.

Volt_Test_Again:
	sbi	ADCSR,ADSC	;ReStart the ADC

Volt_Wait:
	sbic	ADCSR,ADSC	;Loop here till ADSC is zero
	rjmp	Volt_Wait	;

	IN	TEMP,ADCH	;GET 8 BIT RESULT

I always get to this point, indicating that I am indeed talking to the ADC, since the conversion complete bit does clear.
At this point, I only ever get 0x00 in ACCUM.
If I compare to anything >0, then I just loop here forever.

Start_Volt_Test:
	cpi	TEMP,162	;Battery should be greater than 6.0V
	brcs	Volt_Test_Again	;If not, just wait till that happens.