MC68HC908GR8A_07 Datasheet, PDF (51/260 Pages) Freescale Semiconductor, Inc – Microcontrollers

3.6 I/O Signals
The ADC module has six pins shared with port B, PTB5/AD5–PTB0/KBD0.
I/O Signals
3.6.1 ADC Analog Ground Pin (V_SSAD)/ADC Voltage Reference Low Pin (V_REFL)
The ADC analog portion uses V_SSAD as its ground pin and V_REFL as its lower voltage reference pin.
Connect the V_SSAD/V_REFL pin to the same voltage potential as V_SS.
NOTE
For maximum noise immunity, route V_SSAD/V_REFL carefully and 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.
3.6.2 ADC Analog Power Pin (V_DDAD)/ADC Voltage Reference High Pin (V_REFH)
The ADC analog portion uses V_DDAD as its power pin and V_REFH as its upper voltage reference pin.
Connect the V_DDAD/ V_REFH pin to the same voltage potential as V_DD.
NOTE
For maximum noise immunity, route V_DDAD/V_REFH carefully and 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.
3.6.3 ADC Voltage In (V_ADIN)
V_ADIN is the input voltage signal from one of the six ADC channels to the ADC module.
3.7 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADR)
• ADC clock register (ADCLK)
3.7.1 ADC Status and Control Register
Function of the ADC status and control register (ADSCR) is described here.
Address:
Read:
Write:
Reset:
$003C
Bit 7
COCO
R
0
R
6
AIEN
0
= Reserved
5
ADCO
0
4
ADCH4
1
3
ADCH3
1
2
ADCH2
1
1
ADCH1
1
Figure 3-3. 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.
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
Freescale Semiconductor
51