R01UH0823EJ0100 Rev.1.00
Page 1555 of 1823
Jul 31, 2019
RX23W Group
44. 12-Bit A/D Converter (S12ADE)
44.2.14
A/D Sampling State Register n (ADSSTRn) (n = 0 to 7, L, T, O)
The ADSSTRn register sets the sampling time for analog input.
If one state is one ADCLK (A/D conversion clock) cycle and the ADCLK clock is 54 MHz, one state is 18.5 ns. The
initial value is 13 states. If the impedance of analog input signal source is too high to secure sufficient sampling time or if
the ADCLK clock is slow, the sampling time can be adjusted. The ADSSTRn register should be set while the
ADCSR.ADST bit is 0. The lower-limit value for sampling time differs depending on the PCLK to ADCLK frequency
ratio.
Set a value that is 5 states or more when PCLK to ADCLK frequency ratio = 1:1, 2:1, 4:1, or 8:1.
Set a value that is 6 states or more when PCLK to ADCLK frequency ratio = 1:2 or 1:4.
shows the relationship between the A/D sampling state register and the relevant channels.
For details, refer to
section 44.3.6, Analog Input Sampling Time and Scan Conversion Time
.
Note 1. When performing A/D conversion of the temperature sensor output or internal reference voltage, the sampling time should be 5
μs or longer. Since the maximum number of states that can be set by this register is 255, take note of the ADCLK frequency. For
example, when ADCLK = 54 MHz, the sampling time does not reach 5 μs even if 255 states is set.
Address(es): S12AD.ADSSTRL 0008 90DDh, S12AD.ADSSTRT 0008 90DEh, S12AD.ADSSTRO 0008 90DFh,
S12AD.ADSSTR0 0008 90E0h, S12AD.ADSSTR1 0008 90E1h, S12AD.ADSSTR2 0008 90E2h,
S12AD.ADSSTR3 0008 90E3h, S12AD.ADSSTR4 0008 90E4h, S12AD.ADSSTR5 0008 90E5h,
S12AD.ADSSTR6 0008 90E6h, S12AD.ADSSTR7 0008 90E7h
b7
b6
b5
b4
b3
b2
b1
b0
Value after reset:
0
0
0
0
1
1
0
1
Table 44.8
Relationship between A/D Sampling State Register and Relevant Channels
Register Name
Channels
ADSSTR0
AN000
ADSSTR1
AN001
ADSSTR2
AN002
ADSSTR3
AN003
ADSSTR4
AN004
ADSSTR5
AN005
ADSSTR6
AN006
ADSSTR7
AN007
ADSSTRL
AN016 to AN020, AN027
ADSSTRT
Temperature sensor output*
ADSSTRO
Internal reference voltage*