Espressif ESP32 Technical Reference Manual page 643

29 On-Chip Sensors and Analog Signal Processing
Signal Name
VDET_2
VDET_1
32K_XN
32K_XP
SENSOR_VN
SENSOR_CAPN
SENSOR_CAPP
SENSOR_VP
GPIO26
GPIO25
GPIO27
MTMS
MTDI
MTCK
MTDO
GPIO2
GPIO0
GPIO4
Note:
• Some of the SAR ADC2 pins are used as strapping pins (GPIO0, GPIO2, and GPIO15), thus can not be used
freely.
There are five ADC controllers in ESP32: RTC ADC1 CTRL, RTC ADC2 CTRL, DIG ADC1 CTRL, DIG ADC2 CTRL
and PWDET CTRL. The differences between them are summarized in Table 29-3.
DAC
Support deep sleep
ULP coprocessor
PWDET/PKDET
DMA
29.3.4 RTC SAR ADC Controllers
The purpose of SAR ADC controllers in the RTC power domain – RTC ADC1 CTRL and RTC ADC2 CTRL – is to
provide ADC measurement with minimal power consumption in a low frequency.
The outline of a single controller's function is shown in Figure 29-7. For each controller, the start of analog-to-
digital conversion can be triggered by register SENS_SAR_MEASn_START_SAR. The measurement's result can
be obtained from register SENS_SAR_MEASn_DATA_SAR.
The controllers are intertwined with the ULP coprocessor, as the ULP coprocessor has a built-in instruction
Espressif Systems
Table 29-2. Inputs of SAR ADC
ADC Channel #
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
Table 29-3. ESP32 SAR ADC Controllers
RTC ADC1 RTC ADC2
Y -
Y Y
Y Y
- -
- -
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Processed by
SAR ADC1
SAR ADC2
DIG ADC1 DIG ADC2
- -
- -
- -
- -
Y -
ESP32 TRM (Version 5.2)
PWDET
-
-
-
Y
-