The default I2C address for the PCF8523 RTC module is 0x68.
Power
- VB (VBUS) - This is the micro-USB input voltage, connected to the micro-USB port on the Raspberry Pi Pico. It is nominally 5V.
- VS (VSYS) - This is the main system input voltage. It can range from 1.8V to 5.5V and is used to generate the 3.3V needed for the RP2040 and the GPIO pins.
- EN (3V3_EN) - This connects to the enable pin on the Raspberry Pi Pico, and is pulled high (to VSYS) via a 100kΩ resistor.
- 3V - This is the 3.3V output from the Raspberry Pi Pico.
- VR (ADC_VREF) - This is the ADC power supply and reference voltage. It is generated on the Raspberry Pi Pico by filtering the 3.3V supply. It can be used with an external reference when ADC performance is required.
- G - This is the common ground for power and logic. All GND pins are highlighted in white on the silk, with the exception of the ground pins on either side of the SD card slot. They are labeled G.
I2C Logic
- SCL - I2C clock pin on the PiCowbell. It is connected to your microcontroller I2C clock line, which is GPIO5 on the Pico. This connection is shared with the STEMMA QT port on the end of the board.
- SDA - I2C data pin on the PiCowbell. It is connected to your microcontroller I2C data line, which is GPIO4 on the Pico. This connection is shared with the STEMMA QT port on the end of the board.
- STEMMA QT - These connectors allow you to connect to dev boards with STEMMA QT connectors or to other things with various associated accessories. There's one port at the end that connects to your microcontroller. The other four connectors in two rows of two are discussed below.
Duplicate GPIO Hole Pads
The following pads on the PiCowbell Adalogger have a duplicate hole pad next to it for solder-jumpering:
- GP0-GP11, GP20-GP22, Reset, A0-A2, VR, 3V, EN, VS and VB. Ground pins that have a duplicate hole pad are highlighted in white on the silk.
microSD Card SPI
The microSD card slot is connected to the following pins for SPI:
- MI (MISO/GP16) - This is the SPI MISO (Microcontroller In / Serial Out) pin. It's used for the SD card to send data to the microcontroller.
- SCK (GP18) - This is the SPI clock input pin.
- MO (MOSI/GP19) - This is the SPI MOSI (Microcontroller Out / Serial In) pin. It is used to send data from the microcontroller to the SD card.
- CS (Chip Select/GP17) - This is the chip select pin for the SD card.
SD Detect Jumper
On the back of the board, directly above GP15 and to the left of the cowbell logo on the silk, is the SD Detect jumper. The jumper is labeled SD Det on the silk.
You can solder this jumper closed to connect the optional SD card detect line to GP15.
Coin Cell Battery Holder
In the center of the PiCowbell is a holder for a CR1220 coin cell battery. Slot in a CR1220 battery into the holder to use the PCF8523 RTC battery-backup capabilities.
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