MC68HC908GR16A Datasheet, PDF (51/270 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

I/O Registers
3.7.4 ADC Voltage Reference Low Pin (V_REFL)
The ADC analog portion uses V_REFL as its lower voltage reference pin. By default, connect the V_REFH pin
to the same voltage potential as V_SS. External filtering is often necessary to ensure a clean V_REFL for good
results. Any noise present on this pin will be reflected and possibly magnified in A/D conversion values.
NOTE
For maximum noise immunity, route V_REFL carefully and, if not connected
to V_SS, place bypass capacitors as close as possible to the package.
Routing V_REFH close and parallel to V_REFL may improve common mode
noise rejection.
V_SSAD and V_REFL are double-bonded on the MC68HC908GR16A.
3.7.5 ADC Voltage In (V_ADIN)
V_ADIN is the input voltage signal from one of the eight ADC channels to the ADC module.
3.8 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADRH and ADRL)
• ADC clock register (ADCLK)
3.8.1 ADC Status and Control Register
Function of the ADC status and control register (ADSCR) is described here.
Address:
Read:
Write:
Reset:
$003C
Bit 7
6
5
4
3
2
1
COCO
AIEN
ADCO ADCH4 ADCH3 ADCH2 ADCH1
R
0
0
0
1
1
1
1
R = Reserved
Figure 3-4. ADC Status and Control Register (ADSCR)
Bit 0
ADCH0
1
COCO — Conversions Complete Bit
In non-interrupt mode (AIEN = 0), COCO is a read-only bit that is set at the end of each conversion.
COCO will stay set until cleared by a read of the ADC data register. Reset clears this bit.
In interrupt mode (AIEN = 1), COCO is a read-only bit that is not set at the end of a conversion. It
always reads as a 0.
1 = Conversion completed (AIEN = 0)
0 = Conversion not completed (AIEN = 0) or CPU interrupt enabled (AIEN = 1)
NOTE
The write function of the COCO bit is reserved. When writing to the ADSCR
register, always have a 0 in the COCO bit position.
MC68HC908GR16A Data Sheet, Rev. 1.0
Freescale Semiconductor
51