The RS232 port is connected to the UART port on the Raspberry Pi using a MAX3232 interface. The MAX3232 IC converts the 3.3V UART port to RS232 voltages allowing communication with RS232 compatible devices over a DB9 serial cable or with the use of a null-modem cable the board allows terminal access with Linux on the Raspberry Pi using a terminal application. The RS232 port can be accessed through the DB9 port or the solder points on the PCB.
An array of 2.54mm pitch holes with 3.3V and 5V connections are also provided on the PCB allowing you to build additional circuits on the board.
Please note that you can only use one Serial Pi board on a Raspberry Pi. if stacking with other boards we recommend putting the Serial pi at the top of the stack due to the height of the DB9 connector.
Connecting to the RS232 Port
You need to use the latest Raspbian release and disable the built-in Bluetooth to use the Serial Pi Plus on the Raspberry Pi 3 or Raspberry Pi Zero W, see our KB page for the config changes needed.
The RS232 port on the Serial Pi can be accessed through the male DB9 socket or the solder points on the PCB. The DB9 socket is configured as a master socket like you will find on desktop computers allowing you to connect external serial devices with a standard RS232 cable.