Serial Pi Plus

• RS232 Master Serial Port.
• Control the Raspberry Pi over RS232 or connect to external serial accessories.
• Stackable with other Raspberry Pi Hats.
• Mounting holes for use with the AB Electronics UK mounting kits (sold separately)

The Serial Pi Plus is a communication board supporting the RS232 serial protocol, designed for use on the Raspberry Pi and other compatible single-board computers.

RS232 is widely used for connecting computers to devices such as modems, printers, data terminals and various industrial equipment. Despite being an older technology, it remains prevalent in various legacy systems and industrial applications.

The RS232 serial port is connected to the UART port on the Raspberry Pi using a MAX3232 or ICL3232ECBNZ* interface. The MAX3232 and ICL3232ECBNZ* ICs convert the 3.3V UART port to RS232 voltages, allowing communication with RS232 compatible devices over a DB9 serial cable. With a null-modem cable, the board allows terminal access with Linux on the Raspberry Pi using a terminal application.

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 Plus board on a Raspberry Pi. If stacking with other boards, we recommend putting the Serial Pi Plus at the top of the stack due to the height of the DB9 connector.

The RS232 port on the Serial Pi Plus can be accessed through the male DB9 socket or the solder points on the PCB. The DB9 socket is configured as a master socket, as you will find on desktop computers, allowing you to connect external serial devices with a standard RS232 cable.

*Due to global component shortages, Serial Pi Plus boards manufactured after 23/11/2022 may use the Intersil ICL3232ECBNZ RS232 interface IC. The ICL3232ECBNZ is a pin-compatible replacement for the Texas Instruments MAX3232.

Legacy Serial Pi Versions

See our Knowledge Base article for previous versions of this board.

Technical Details

Assembly Instructions

The Serial Pi Plus is supplied with the 40-pin GPIO connector, and the DB9 connector is unsoldered. 

Before using the Serial Pi Plus, you need to solder both connectors onto the PCB. We suggest soldering the 40-pin GPIO connector first and then the DB9 connector. 

To make assembly easier, we have designed a PCB header assembly jig which you can download and print.

Watch the assembly video, best viewed in 1080p high-quality mode:

Watch our assembly guide on YouTube. (opens in a new window)

PCB Header Assembly Jig

Download and print our PCB Header Assembly Jig to hold your circuit board when soldering the header pins.

RS232 Port

The pin-out connections for the RS232 port are shown below:

Pin	Usage
1	N/C
2	RX (data receive)
3	TX (data transmit)
4	N/C
5	Ground
6	N/C
7	N/C
8	N/C
9	N/C

DB9 connector as viewed from the front of the Serial Pi Plus

Using the RS232 port for terminal connections

The RS232 port can be used for remote terminal connections on the Raspberry Pi, allowing remote access and control without needing an ethernet connection. You will need to use a Null-Modem cable to connect the Serial Pi to a desktop computer. A wiring diagram for making a Null-Modem cable can be found below. For details on configuring the RS232 communication on the Raspberry Pi, visit our knowledge base.

Null-Modem Cable

Null model connections

Connector 1	Connector 2	Function
2	3	Rx ← Tx
3	2	Tx → Rx
5	5	Ground