I’m trying to understand the signal mapping between the XIAO-ESP32C6 module and the ESP32-C6FH4 chip used on the module. More specifically, and referring to the below diagram, I’m trying to figure out what the labels beginning with “PA” refer to. For example, what does PA02 refer to for pin 1? Thanks!
Hi there,
And Welcome Here…
So As shown each PAxx/PBxx label maps to a specific ESP32-C6 GPIO. Developers can use the ESP32-C6’s GPIO numbers or the XIAO’s D/A labels interchangeably in code (the Arduino core variant defines D0–D10 accordinglysigmdel.ca). The PAxx naming is simply a schematic label – for practical use on the XIAO ESP32C6 board, refer to the GPIO numbers or XIAO D#/A# designators listed.
Complete Pin Mapping and References
For clarity, here’s a summary confirming the mapping from PAxx labels to ESP32-C6 GPIO using official sources:
- PA02 → GPIO0: XIAO pin D0/A0. (PA02 was Port A pin 02 on SAMD21wiki.seeedstudio.com, now tied to ESP32-C6 GPIO0sigmdel.ca.)
- PA08 → GPIO22: XIAO pin D4 (I2C SDA). (PA08 was Port A pin 08 on SAMD21wiki.seeedstudio.com, now ESP32-C6 GPIO22 used for SDA).
- PA09 → GPIO23: XIAO pin D5 (I2C SCL). (Port A pin 09 on SAMD21, now ESP32-C6 GPIO23 for SCL).
- PA10 → GPIO2: XIAO pin D2/A2. (Port A pin 10 on SAMD21, now ESP32-C6 GPIO2)wiki.seeedstudio.comsigmdel.ca.
- PA11 → GPIO21: XIAO pin D3. (Port A pin 11 on SAMD21, now ESP32-C6 GPIO21)wiki.seeedstudio.com.
- PA04 → GPIO1: XIAO pin D1/A1. (Port A pin 04 on SAMD21, now ESP32-C6 GPIO1)wiki.seeedstudio.comsigmdel.ca.
- PA05 → GPIO20: XIAO pin D9 (SPI MISO). (Port A pin 05 on SAMD21, now ESP32-C6 GPIO20)wiki.seeedstudio.com.
- PA06 → GPIO18: XIAO pin D10 (SPI MOSI). (Port A pin 06 on SAMD21, now ESP32-C6 GPIO18)wiki.seeedstudio.com.
- PA07 → GPIO19: XIAO pin D8 (SPI SCK). (Port A pin 07 on SAMD21, now ESP32-C6 GPIO19)wiki.seeedstudio.com.
- PB08 → GPIO16: XIAO pin D6 (UART TX). (Port B pin 08 on SAMD21, now ESP32-C6 GPIO16)wiki.seeedstudio.com.
- PB09 → GPIO17: XIAO pin D7 (UART RX). (Port B pin 09 on SAMD21, now ESP32-C6 GPIO17)wiki.seeedstudio.com.
The “PAxx” labels (e.g. PA02, PA08) on the XIAO ESP32C6 pinout are a legacy from Seeed’s original XIAO board (which used an ATSAMD21 microcontroller). “PA” denotes Port A on the ATSAMD21 MCU, and the number is the MCU’s pin number on that port. In other words, the XIAO form-factor pins were initially named after the SAMD21’s port pins. For example, the original XIAO had:
- PA02 for the pin corresponding to XIAO digital/analog pin 0wiki.seeedstudio.com
- PA08 for the pin corresponding to XIAO digital pin 4wiki.seeedstudio.com
These PAxx names appear on the XIAO ESP32C6 schematic/pinout to label the same physical pins, even though the ESP32-C6 chip itself does not have “PA” ports. They are effectively placeholders carried over from the SAMD21 naming convention on the board.
Mapping PAxx to ESP32-C6 GPIO Numbers
On the XIAO ESP32C6, each PAxx-labeled pin is wired to a specific ESP32-C6 GPIO. Below is the mapping between the module’s PA-labels (XIAO pin names) and the actual ESP32-C6 GPIO numbers, along with typical functions:
| XIAO Pin | Legacy Label | ESP32-C6 GPIO | Typical Functions |
|---|---|---|---|
| D0 / A0 | PA02 | GPIO0 | ADC1_CH0, GPIO0docs.espressif.com (available as digital I/O or analog in) |
| D1 / A1 | PA04 | GPIO1 | ADC1_CH1, GPIO1 (digital/analog)docs.espressif.com |
| D2 / A2 | PA10 | GPIO2 | ADC1_CH2, GPIO2 (digital/analog)docs.espressif.com |
| D3 | PA11 | GPIO21 | Digital I/O, used as SPI (SDIO_DATA1) on ESP32-C6. |
| D4 (SDA) | PA08 | GPIO22 | I²C SDA (default), digital I/O (SPI SDIO_DATA2). |
| D5 (SCL) | PA09 | GPIO23 | I²C SCL (default), digital I/O (SPI SDIO_DATA3). |
| D6 (TX0) | PB08 | GPIO16 | UART0 TX (U0TXD), digital I/O. |
| D7 (RX0) | PB09 | GPIO17 | UART0 RX (U0RXD), digital I/O. |
| D8 (SCK) | PA07 | GPIO19 | SPI SCK (SDIO_CLK), digital I/O. |
| D9 (MISO) | PA05 | GPIO20 | SPI MISO (SDIO_DATA0), digital I/O. |
| D10 (MOSI) | PA06 | GPIO18 | SPI MOSI (SDIO_CMD), digital I/O. |
The typical functions listed (UART, I²C, SPI, ADC) are how Seeed configured the XIAO ESP32C6 by default: for instance, D6/D7 (which were PB08/PB09 on the SAMD21) are tied to the ESP32-C6’s UART0 for serial TX/RX, and D4/D5 (PA08/PA09) are used as the I²C SDA/SCL lines (ESP32-C6 GPIO22/23). D0–D2 (PA02, PA04, PA10) are connected to ESP32-C6 GPIO0–GPIO2, which support ADC input (channels 0–2) and are labeled A0–A2 for analog use
HTH
GL 
PJ 
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If you look at the schematic for XIAO_MG24, you will see the exact same block drawn as U4, which I suspect was copy-pasted and used when drawing the schematic for XIAO_ESP32C6.
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Thank you very much!
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