XC886/888CLM
Analog-to-Digital Converter
User’s Manual
16-4
V1.3, 2010-02
ADC, V 1.0
For module clock
f
ADC
= 24 MHz, the analog clock
f
ADCI
frequency can be selected as
shown in
As
f
ADCI
cannot exceed 10 MHz, bit field CTC should not be set to 00
B
when
f
ADC
is
24 MHz. During slow-down mode where
f
ADC
may be reduced to 12 MHz, 6 MHz etc.,
CTC can be set to 00
B
as long as the divided analog clock
f
ADCI
does not exceed 10 MHz.
However, it is important to note that the conversion error could increase due to loss of
charges on the capacitors, if
f
ADC
becomes too low during slow-down mode.
16.2.1
Conversion Timing
The analog-to-digital conversion procedure consists of the following phases:
•
Synchronization phase (
t
SYN
)
•
Sample phase (
t
S
)
•
Conversion phase
•
Write result phase (
t
WR
)
Figure 16-3
Conversion Timing
Table 16-1
f
ADCI
Frequency Selection
Module Clock
f
ADC
CTC
Prescaling Ratio
Analog Clock
f
ADCI
24 MHz
00
B
÷ 2
12 MHz (N.A)
01
B
÷ 3
8 MHz
10
B
÷ 4
6 MHz
11
B
(default)
÷ 32
750 kHz
t
S
t
CONV
t
WR
SAMPLE Bit
BUSY Bit
Conversion Phase
Sample Phase
Write Result Phase
conversion start
trigger
Source
interrupt
Result
interrupt
t
SYN
Channel
interrupt
f
ADCI
*