Strapping Pins - Espressif Systems ESP32 Series Manual

2.3 Strapping Pins

Name No.
SD_DATA_0 32
SD_DATA_1 33
GPIO5 34
GPIO18 35
GPIO23 36
VDD3P3_CPU 37
GPIO19 38
GPIO22 39
U0RXD 40
U0TXD 41
GPIO21 42
VDDA 43
XTAL_N 44
XTAL_P 45
VDDA 46
CAP2 47
CAP1 48
GND 49
Notice:
GPIO36, GPIO37, GPIO38, GPIO39, GPIO34 and GPIO35 can only be used for input.
2.3 Strapping Pins
ESP32 has six strapping pins:
• MTDI/GPIO12: internal pull-down
• GPIO0: internal pull-up
• GPIO2: internal pull-down
• GPIO4: internal pull-down
• MTDO/GPIO15: internal pull-up
• GPIO5: internal pull-up
Software can read the value of these six bits from the register "GPIO_STRAPPING".
During the chip power-on reset, the latches of the strapping pins sample the voltage level as strapping bits of "0"
or "1", and hold these bits until the chip is powered down or shut down. The strapping bits configure the device
boot mode, the operating voltage of VDD_SDIO and other system initial settings.
Espressif Systems
Type Function
I/O GPIO7, SD_DATA0, SPIQ, HS1_DATA0, U2RTS
I/O GPIO8, SD_DATA1, SPID, HS1_DATA1, U2CTS
VDD3P3_CPU
I/O GPIO5, VSPICS0, HS1_DATA6, EMAC_RX_CLK
I/O GPIO18, VSPICLK, HS1_DATA7
I/O GPIO23, VSPID, HS1_STROBE
P CPU IO power supply input (1.8V
I/O GPIO19, VSPIQ, U0CTS, EMAC_TXD0
I/O GPIO22, VSPIWP, U0RTS, EMAC_TXD1
I/O GPIO3, U0RXD, CLK_OUT2
I/O GPIO1, U0TXD, CLK_OUT3, EMAC_RXD2
I/O GPIO21, VSPIHD, EMAC_TX_EN
Analog
I/O Analog power supply (2.3V - 3.6V)
O External crystal output
I External crystal input
P Power supply for PLL (2.3V
Connects with a 3 nF capacitor and 20 kΩ resistor in parallel to
I
CAP1
I Connects with a 10 nF series capacitor to ground
GND
P GND
11
2 PIN DEFINITIONS
~ 3.3V)
~ 3.6V)
ESP32 Hardware Design Guideline V1.0