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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
The Analog/Digital Converter
User’s Manual
16-19
V2.2, 2004-01
ADC_X1, V2.1
Standard Timing Control
Standard timing control is performed by using two 2-bit fields in register ADC_CON.
Bitfield ADCTC (conversion time control) selects the basic conversion clock (
f
BC
), used
for the operation of the A/D converter. The sample time is derived from this conversion
clock and controlled by bitfield ADSTC. The sample time is always a multiple of 8
f
BC
periods.
lists the possible combinations.
Improved Timing Control
To provide a finer resolution for programming of the timing parameters, wider bitfields
have been implemented for timing control (the 2-bit bitfields in register ADC_CON are
disregarded in all cases).
In compatibility mode (with bit ICST = 1), the bitfields in register ADC_CON1 are used
for all conversions.
In enhanced mode (bit MD = 1), the bitfields in register ADC_CTR2 are used for
standard conversions. Injected conversions use the bitfields in register ADC_CTR2IN.
Bitfield ADCTC (conversion time control) selects the basic conversion clock (
f
BC
), used
for the operation of the A/D converter. The sample time is derived from this conversion
clock and controlled by bitfield ADSTC. The sample time is always a multiple of 4
f
BC
periods.
lists the possible combinations.
Table 16-3
Standard Conversion and Sample Timing
Control
ADC_CON.15|14
(ADCTC)
A/D Converter
Basic Clock
f
ADC_CON.13|12
(ADSTC)
Sample Time
t
S
00
f
ADC
/4
00
t
BC
×
8
01
f
ADC
/2
01
t
BC
×
16
10
f
ADC
/16
10
t
BC
×
32
11
f
ADC
/8
11
t
BC
×
64
Table 16-4
Improved Conversion and Sample Timing
Control
ADCTC
A/D Converter
Basic Clock
f
BC
1)
1) The limit values for
f
BC
(see data sheet) must not be exceeded when selecting ADCTC and
f
ADC
.
ADSTC
Sample Time
t
S
00’0000
B
= 00
H
f
ADC
/1
00’0000
B
= 00
H
t
BC
×
8
00’0001
B
= 01
H
f
ADC
/2
00’0001
B
= 01
H
t
BC
×
12
00’0010
B
= 02
H
f
ADC
/3
00’0010
B
= 02
H
t
BC
×
16
…
f
ADC
/(ADCTC + 1)
…
t
BC
×
4
×
(ADSTC + 2)
11’1111
B
= 3F
H
f
ADC
/64
11’1111
B
= 3F
H
t
BC
×
260