MC68HC908AT32 Datasheet, PDF (228/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Analog-to-Digital Converter (ADC-8)
21.6 I/O Signals
The ADC module has eight channels that are shared with I/O ports B. Refer to 29.6 ADC Characteristics
for voltages referenced below.
21.6.1 ADC Analog Power Pin (V_DDAREF)/ADC Voltage Reference Pin (V_REFH)
The ADC analog portion uses V_DDAREF as its power pin. Connect the A_VDD/V_DDAREF pin to the same
voltage potential as V_DD. External filtering may be necessary to ensure clean V_DDAREF for good results.
V_REFH is the high reference voltage for all analog-to-digital conversions. Connect the V_REFH pin to a
voltage potential between 1.5 volts and V_DDAREF/A_VDD depending on the desired upper conversion
boundary.
NOTE
Route V_DDAREF carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
21.6.2 ADC Analog Ground Pin (A_VSS)/ADC Voltage Reference Low Pin (V_REFL)
The ADC analog portion uses A_VSS as its ground pin. Connect the A_VSS pin to the same voltage potential
as V_SS.
V_REFL is the lower reference supply for the ADC.
21.6.3 ADC Voltage In (ADCVIN)
ADCVIN is the input voltage signal from one of the eight ADC channels to the ADC module.
21.7 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 (ADICLK)
21.7.1 ADC Status and Control Register
The following paragraphs describe the function of the ADC status and control register.
Address:
Read:
Write:
Reset:
$0038
Bit 7
COCO
R
0
R
6
5
AIEN
ADCO
0
0
= Reserved
4
ADCH4
1
3
ADCH3
1
2
ADCH2
1
1
ADCH1
1
Figure 21-2. ADC Status and Control Register (ADSCR)
Bit 0
ADCH0
1
MC68HC908AT32 Data Sheet, Rev. 3.1
228
Freescale Semiconductor