XC886/888CLM
Analog-to-Digital Converter
User’s Manual
16-3
V1.3, 2010-02
ADC, V 1.0
16.2
Clocking Scheme
A common module clock f
ADC
generates the various clock signals used by the analog and
digital parts of the ADC module:
•
f
ADCA
is input clock for the analog part.
•
f
ADCI
is internal clock for the analog part (defines the time base for conversion length
and the sample time). This clock is generated internally in the analog part, based on
the input clock
f
ADCA
to generate a correct duty cycle for the analog components.
•
f
ADCD
is input clock for the digital part. This clock is used for the arbiter (defines the
duration of an arbitration round) and other digital control structures (e.g., registers
and the interrupt generation).
The internal clock for the analog part
f
ADCI
is limited to a maximum frequency of 10 MHz.
Therefore, the ADC clock prescaler must be programmed to a value that ensures
f
ADCI
does not exceed 10 MHz. The prescaler ratio is selected by bit field CTC in register
GLOBCTR. A prescaling ratio of 32 can be selected when the maximum performance of
the ADC is not required.
Figure 16-2
Clocking Scheme
analog
components
f
ADCI
f
ADC
= f
PCLK
MUX
arbiter
registers
interrupts
analog part
digital part
f
ADCD
f
ADCA
32
÷
4
÷
3
÷
clock prescaler
CTC
≤
Condition: f
ADCI
10 MHz, where t
ADCI =
f
ADCI
1
2
÷
*
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