R01UH0823EJ0100 Rev.1.00
Page 1607 of 1823
Jul 31, 2019
RX23W Group
44. 12-Bit A/D Converter (S12ADE)
44.3.5.4
Restrictions for Compare Function
The following restrictions are provided for the compare function.
1. The compare function must not be used together the self-diagnosis function or double trigger mode. (The compare
function is not available for the ADRD register and the ADDBLDR register.)
2. Specify single scan mode when using match/mismatch event outputs.
3. When temperature sensor or internal reference voltage is selected for window A, window B operations are disabled.
4. When temperature sensor or internal reference voltage is selected for window B, window A operations are disabled.
5. It is prohibited to set the same channel for window A and window B.
6. When using the buffer function, specify single scan mode. (It is also prohibited to use double trigger mode
together.)
7. Set the reference voltage values so that the high-side reference voltage value is equal to or larger than the low-side
reference voltage value.
44.3.6
Analog Input Sampling Time and Scan Conversion Time
Scan conversion can be activated either by software, synchronous trigger, or asynchronous trigger input. After the start-
of-scanning-delay time (t
D
) has elapsed, processing for disconnection detection assistance and processing of conversion
for self-diagnosis proceed, and this is followed by processing for A/D conversion.
shows the scan conversion timing in single scan mode, in which scan conversion is activated by software
or a synchronous trigger.
shows the scan conversion timing in single scan mode, in which scan conversion
is activated by an asynchronous trigger. The scan conversion time (t
SCAN
) includes the start-of-scanning-delay time (t
D
),
disconnection detection assistance processing time (t
DIS
, self-diagnosis A/D conversion processing time (t
DIAG
)
, A/
D conversion processing time (t
CONV
), and end-of-scanning-delay time (t
ED
).
The A/D conversion processing time (t
CONV
) consists of sampling time (t
SPL
) and time for conversion by successive
approximation (t
SAM
). The sampling time (t
SPL
) is used to charge sample-and-hold circuits in the A/D converter. If there
is not sufficient sampling time due to the high impedance of an analog input signal source, or if the A/D conversion clock
(ADCLK) is slow, sampling time can be adjusted using the ADSSTRn register.
The time for conversion by successive approximation (t
SAM
) is at 32 ADCLK states during high-speed conversion
operation, and 41 ADCLK states during low-current conversion operation.
shows the scan conversion time.
The scan conversion time (t
SCAN
) in single scan mode for which the number of selected channels is n can be determined
as follows:
t
SCAN
= t
D
+ (t
DIS
× n) + t
DIAG
+ (t
CONV
× n)
+ t
ED
The scan conversion time for the first cycle in continuous scan mode is t
SCAN
for single scan minus t
ED
.
The scan conversion time for the second and subsequent cycles in continuous scan mode is fixed to (t
DIS
× n) + t
DIAG
+
t
DSD
+ (t
CONV
× n).
Note 1. When disconnection detection assistance is not selected, t
DIS
= 0. The auto-discharge period of 15 ADCLK
states is inserted only when the temperature sensor or internal reference voltage is A/D-converted.
Note 2. When the self-diagnosis function is not used, t
DIAG
= 0, t
DSD
= 0.
Note 3. t
CONV
× n when the sampling time (t
SPL
) of selected channels is the same, but it is the total of the sampling time
of each channel and time for conversion by successive approximation (t
SAM
).