MISO Pin Functionality Overview

Worked for 4 mins 52 sec

flux

On this ESP-12E part, MISO is pin 10, which maps to GPIO12 / MTDI / HSPI_MISO.

What it does

Primary SPI role: MISO = Master In, Slave Out.
If the ESP8266 is acting as the SPI master, this pin is the data input back into the ESP8266 from the SPI peripheral.
GPIO role: It can also be used as a normal general-purpose digital I/O when SPI is not using it.
Alternate functions: The ESP8266 datasheet also lists this pad for other multiplexed functions such as I2S data input and PWM.

Electrical characteristics

From the ESP8266EX datasheet, this pin is a 3.3 V-class digital I/O:

Operating I/O supply: tied to the chip’s I/O domain, with device working voltage 2.5 V to 3.6 V, typically 3.3 V
Input low threshold (VIL): up to 0.25 × VIO
Input high threshold (VIH): from 0.75 × VIO
Output low (VOL): up to 0.1 × VIO
Output high (VOH): at least 0.8 × VIO
Max output drive current: 12 mA
It is not 5 V tolerant. Drive it only with 3.3 V logic.

Special considerations

Boot/reset caution: GPIO12 is a multifunction boot-sensitive pin in many ESP8266 designs, so avoid forcing it strongly to the wrong level during power-up/reset.
If used for SPI: connect it only to the peripheral’s MISO/output pin, and make sure no other device drives the line at the same time unless you’re intentionally sharing the SPI bus.
If used as GPIO: confirm your firmware muxes the pin away from HSPI first.
Avoid heavy loads: it is a logic pin, not a power output.

Practical usage rule

Use this pin for:

HSPI MISO when talking to SPI sensors/displays/memory, or
general 3.3 V digital I/O if SPI is unused.

Do not use it for:

direct 5 V interfaces
loads needing more than a few mA
circuitry that may hold it in an unsafe state during reset.

Check boot straps

Run SPI ERC

Explain MOSI

MISO pull resistor

Compare SPI pins

GPIO1/TXD

GPIO13

GPIO2

CS0

GPIO12

MISO

ADC

SCLK

VCC

GPIO16

MOSI

GPIO14

GPIO9

GPIO3/RXD

GPIO4

GND

GPIO10

~{RST}

GPIO0

GPIO5

GPIO15

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