Analog-to-Digital Converter (ADC12)
MCF51CN128 Reference Manual, Rev. 6
Freescale Semiconductor
15-11
15.4
Functional Description
The ADC module is disabled during reset or when the ADCH bits are all high. The module is idle when a
conversion has completed and another conversion has not been initiated. When idle, the module is in its
lowest power state.
The ADC can perform an analog-to-digital conversion on any of the software selectable channels. In 12-bit
and 10-bit mode, the selected channel voltage is converted by a successive approximation algorithm into
a 12-bit digital result. In 8-bit mode, the selected channel voltage is converted by a successive
approximation algorithm into a 9-bit digital result.
3:2
MODE
Conversion Mode Selection. MODE bits are used to select between 12-, 10-, or 8-bit operation. See
1:0
ADICLK
Input Clock Select. ADICLK bits select the input clock source to generate the internal clock ADCK. See
.
Table 15-7. Clock Divide Select
ADIV
Divide Ratio
Clock Rate
00
1
Input clock
01
2
Input clock
÷
2
10
4
Input clock
÷
4
11
8
Input clock
÷
8
Table 15-8. Conversion Modes
MODE
Mode Description
00
8-bit conversion (N=8)
01
12-bit conversion (N=12)
10
10-bit conversion (N=10)
11
Reserved
Table 15-9. Input Clock Select
ADICLK
Selected Clock Source
00
Bus clock
01
Bus clock divided by 2
10
Alternate clock (ALTCLK)
11
Asynchronous clock (ADACK)
Table 15-6. ADCCFG Register Field Descriptions (continued)
Field
Description