R8C/1A Group, R8C/1B Group
17. A/D Converter
Rev.1.30
Dec 08, 2006
Page 240 of 315
REJ09B0252-0130
17.3
Sample and Hold
When the SMP bit in the ADCON2 register is set to 1 (sample and hold function enabled), the A/D conversion rate
per pin increases to 28
φ
AD cycles for 8-bit resolution or 33
φ
AD cycles for 10-bit resolution. The sample and hold
function is available in all operating modes. Start A/D conversion after selecting whether the sample and hold
circuit is to be used or not.
When performing A/D conversion, charge the comparator capacitor in the MCU during the sampling time.
Figure 17.6 shows a Timing Diagram of A/D Conversion.
Figure 17.6
Timing Diagram of A/D Conversion
17.4
A/D Conversion Cycles
Figure 17.7 shows the A/D Conversion Cycles.
Figure 17.7
A/D Conversion Cycles
Sampling time
4ø AD cycles
Sample and Hold
disabled
Conversion time of 1st bit
2nd bit
Comparison
time
Sampling time
2.5ø AD cycles
Comparison
time
Sampling time
2.5ø AD cycles
Comparison
time
* Repeat until conversion ends
Sampling time
4ø AD cycles
Sample and Hold
enabled
Conversion time of 1st bit
2nd bit
Comparison
time
Comparison
time
Comparison
time
* Repeat until conversion ends
Comparison
time
A/D Conversion Mode
Without sample and hold
Without sample and hold
With sample and hold
With sample and hold
8 bits
10 bits
8 bits
10 bits
Conversion
Time
Comparison
Time
Comparison
Time
End
Processing
Sampling
Time
End of
processing
Conversion time of 1st bit
Sampling
Time
Conversion time 2nd and
following bits
49
φ
AD
4
φ
AD
2.0
φ
AD
2.5
φ
AD
2.5
φ
AD
8.0
φ
AD
59
φ
AD
4
φ
AD
2.0
φ
AD
2.5
φ
AD
2.5
φ
AD
8.0
φ
AD
28
φ
AD
4
φ
AD
2.5
φ
AD
0.0
φ
AD
2.5
φ
AD
4.0
φ
AD
33
φ
AD
4
φ
AD
2.5
φ
AD
0.0
φ
AD
2.5
φ
AD
4.0
φ
AD