Espressif ESP32 Technical Reference Manual page 50

4 IO_MUX and GPIO Matrix (GPIO, IO_MUX)
peripheral output signals.
See Section 4.9 for a list of GPIO Matrix peripheral signals.
3. RTC IO_MUX is used to connect GPIO pads to their low-power and analog functions. Only a subset of
GPIO pads have these optional "RTC" functions.
See Section 4.11 for a list of RTC IO_MUX functions.
4.2 Peripheral Input via GPIO Matrix
4.2.1 Summary
To receive a peripheral input signal via the GPIO Matrix, the GPIO Matrix is configured to source the peripheral
signal's input index (0-18, 23-36, 39-58, 61-90, 95-124, 140-155, 164-181, 190-195, 198-206) from one of the 34
GPIOs (0-19, 21-23, 25-27, 32-39).
The input signal is read from the GPIO pad through the IO_MUX. The IO_MUX must be configured to set the
chosen pad to "GPIO" function. This causes the GPIO pad input signal to be routed into the GPIO Matrix, which
in turn routes it to the selected peripheral input.
4.2.2 Functional Description
Figure 4-2 shows the logic for input selection via GPIO Matrix.
To read GPIO pad X into peripheral signal Y, follow the steps below:
1. Configure the GPIO_FUNCy_IN_SEL_CFG register corresponding to peripheral signal
• Set GPIO_SIGy_IN_SEL to enable peripheral signal input via GPIO matrix.
• Set the GPIO_FUNCy_IN_SEL field in this register, corresponding to the GPIO pad
2. Configure the GPIO_FUNCx_OUT_SEL_CFG register and clear the GPIO_ENABLE_DATA[x] field correspond-
ing to GPIO pad X in the GPIO Matrix:
• Set the GPIO_FUNCx_OEN_SEL bit in the GPIO_FUNCx_OUT_SEL_CFG register to force the pin's
output state to be determined always by the GPIO_ENABLE_DATA[x] field.
Espressif Systems
Figure 4-2. Peripheral Input via IO_MUX, GPIO Matrix
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Y in the GPIO Matrix:
X to read from.
ESP32 TRM (Version 5.2)