Espressif Systems ESP32 Technical Reference Manual page 29

4. IO_MUX and GPIO Matrix
4.1 Introduction
The ESP32 chip features 40 physical GPIO pads. Some GPIO pads cannot be used or do not have the
corresponding pin on the chip package. Each pad can be used as a general purpose I/O or can be connected to
an internal peripheral signal. The IO_MUX, RTC IO_MUX and the GPIO matrix are responsible for routing signals
from the peripherals to GPIO pads. Together these systems provide highly configurable I/O.
This chapter describes the signal selection and connection between the digital pads (FUNC_SEL, IE, OE, WPU,
WDU, etc), 256 peripheral input/output signals (control signals: SIG_IN_SEL, SIG_OUT_SEL, IE, OE, etc), fast
peripheral input/output signals (control signals: SIG_IN_SEL, SIG_OUT_SEL, IE, OE, etc), and RTC
IO_MUX.
Figure 6: IO_MUX, RTC IO_MUX and GPIO Matrix Overview
1. The IO_MUX contains one register per GPIO pad. Each pad can be configured for "GPIO" function
(connected to the GPIO Matrix) or configured for a direct function (bypassing the GPIO Matrix. Some high
speed digital functions (Ethernet, SDIO, SPI, JTAG, UART) can bypass the GPIO Matrix for better high
frequency digital performance. In this case, the IO_MUX is used to connect these pads directly to the
peripheral.)
Refer to Section 4.10
2. The GPIO Matrix is a full switching matrix between the peripheral input/output signals and the pads.
• For input to the chip: Each of the 256 internal peripheral inputs can select any GPIO pad as the input
source.
• For output from the chip: The output signal of each of the 40 GPIO pads can be from one of the 256
peripheral output signals.
Refer to Section 4.9
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.
Espressif Systems
for a list of IO_MUX functions for each I/O pad.
for a list of GPIO Matrix peripheral signals.
28 ESP32 Technical Reference Manual V1.0
4 IO_MUX AND GPIO MATRIX