
Analog-to-Digital Converter (ADC)
MC68HC908GP32 MC68HC08GP32 Data Sheet, Rev. 7
58
Freescale Semiconductor
5.6.2 ADC Analog Ground Pin (VSSAD)/ADC Voltage Reference Low Pin (VREFL)
The ADC analog portion uses VSSAD as its ground pin. Connect the VSSAD pin to the same voltage
potential as VSS.
NOTE
Route VSSAD cleanly to avoid any offset errors.
5.6.3 ADC Voltage In (VADIN)
VADIN is the input voltage signal from one of the eight ADC channels to the ADC module.
5.7 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)
5.7.1 ADC Status and Control Register
Function of the ADC status and control register (ADSCR) is described here.
COCO — Conversions Complete
When the AIEN bit is a logic 0, the COCO is a read-only bit which is set each time a conversion is
completed except in the continuous conversion mode where it is set after the first conversion. This bit
is cleared whenever the ADSCR is written or whenever the ADR is read.
If the AIEN bit is a logic 1, the COCO becomes a read/write bit, which should be cleared to logic 0 for
CPU to service the ADC interrupt request. Reset clears this bit.
1 = Conversion completed (AIEN = 0)
0 = Conversion not completed (AIEN = 0)/CPU interrupt (AIEN = 1)
AIEN — ADC Interrupt Enable Bit
When this bit is set, an interrupt is generated at the end of an ADC conversion. The interrupt signal is
cleared when the data register is read or the status/control register is written. Reset clears the AIEN bit.
1 = ADC interrupt enabled
0 = ADC interrupt disabled
ADCO — ADC Continuous Conversion Bit
When set, the ADC will convert samples continuously and update the ADR register at the end of each
conversion. Only one conversion is completed between writes to the ADSCR when this bit is cleared.
Reset clears the ADCO bit.
1 = Continuous ADC conversion
0 = One ADC conversion
Address:
$003C
Bit 7
654321
Bit 0
Read:
COCO
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
Write:
Reset:
00011111
Figure 5-2. ADC Status and Control Register (ADSCR)