P1AM-SERIAL Doubler

Sometimes you just need more serial ports! Between modbus, SCPI, ASCII, and the hundred other protocols that work via RS232, sometimes you just can't combine different protocols and need more physical ports. Fear no more! I've done all of the heavy lifting for you. I've designed a circuit board and modified the code for this library to enable to usage of another P1AM-Serial module expanding the amount of ports from 2 to 4! See the wiki for photos.

Under the Hood:

At its core, the P1AM is a SAMD21G18, which is the same IC that runs the Arduino Zero. If you check into the documentation for the SAMD21, you'll see that is has 6 "sercom" ports. In other words, it has 6 different ports that are configurable to be GPIO pins, UART, I2C, or SPI pins. What I've done is enabled an unsused port, and hijacked the I2C port and reconfigured it to be a serial UART port for us. All of this might sound quite scary, and honestly, it is. Good news is you can skip all the technical and get right to it if you don't need additional information.

Sercom0 is being used for I2C, so we're gonna hijack that, and Sercom4 is completely free. In order to remap these, we have to access the variant.h & variant.cpp board files of the P1AM. The new mappings are as shown:

Sercom#/[Pad#]	Arduino Port	DigitalPin	PriorFunc	NewFunc
Sercom0/[P0]	PortA8	D11	SDA	Serial3 TX
Sercom0/[P1]	PortA9	D12	SCL	Serial3 RX
Sercom4/[P2]	PortB10	D4	N/A	Serial4 TX
Sercom4/[P3]	PortB11	D5	N/A	Serial4 RX

All of these definitions are updated in the variants.h & .cpp accordingly. Please note, I2C will no longer function, and the only free available pin on the module is Pin #7. We are using all of the available expansion pins for enabling the use of the second P1AM-Serial module.

Adapter Assembly and Installation:

For pictures and more information see this repository's wiki. The adapter board files are in this repository under "hardware." Within that folder, there are DXF board outlines, GERBER files, Eagle files, and Fusion360 files. PCBs can be ordered very cheaply from places like JLCpcb or PCBWay for less than $20. Obviously through-hole pin headers couldn't be use as the pins connections needed to be rearranged for the secondary module. So "splayed leg" 2.54mm pitch pin headers were used instead. The "splayed leg" male pin headers are available for purchase from Digikey, manufacturer part # M20-8771042, Digikey part # 952-3263-ND. The female pin headers are just your normal headers with the pins splayed out manually with a pair of pliers. Make sure the female headers go on the side of the PCB with the text. It only takes a minute or two to do. After soldering the board up, simply plug the adapter into the side of the P1AM-Serial just like it's another module. Then plug the secondary P1AM-Serial module into the other side.

Usage

You must install my version of the P1AM library (P1AM_Doubler and the P1AM-Serial_Doubler. These can both be found in my repositories. Before installation of these, please remove the existing libraries for the P1AM & P1AM-SERIAL.

RS485 was NOT tested, only RS232 on the additional two ports. Unfortunately I don't have a way to test the RS485, but I added all the support in the code for it, so it should work :).

The code snippets below require the P1AM_4x_Serial library. Use of the P1AM_4x_Serial library requires version 1.6.21 or greater of the P1AM-100 in the Arduino boards manager.

When using the P1AM Serial with a custom protocol, i.e. writing data directly to the port, use the function below that corresponds to the port and mode you are using to configure the port. Baudrate and other settings can be configured the same way as the standard Arduino Serial library. For a list of all configuration options click here.

• PORT1_RS485_BEGIN()
• PORT1_RS232_BEGIN()
• PORT2_RS485_BEGIN()
• PORT2_RS232_BEGIN()
• PORT3_RS485_BEGIN()
• PORT3_RS232_BEGIN()
• PORT4_RS485_BEGIN()
• PORT4_RS232_BEGIN()

Once the port is configured, use the Port1, Port2, Port3, & Port4 objects to interact with the ports. Of course Port3 is the first port on the second serial module, and Port4 is the second port on the second serial module.

// Configure both ports for RS485 at 9600 baud, 8 data bits, no parity, 1 stop bit
PORT1_RS485_BEGIN(9600, SERIAL_8N1);
PORT2_RS485_BEGIN(9600);// 8N1 is the default setting
PORT3_RS232_BEGIN(115200, SERIAL_8N1);  
PORT4_RS232_BEGIN(115200, SERIAL_8N1);

// Start RS485 transmission
Port1.beginTransmission();
Port2.beginTransmission();
Port3.beginTransmission();
Port4.beginTransmission();

// Use Ports 1-4 to write to the ports
Port1.write("Hello World 1\r\n");
Port2.write("Hello World 2\r\n");
Port3.write("Hello World 3\r\n");
Port4.write("Hello World 4\r\n");

Additionally, you can use the standard Serial1, Serial2, Serial3, & Serial4 objects to interact with the ports, however when doing so you cannot use any RS485 functions such as beginTransmission() or endTransmission().

// Configure all ports for RS232 at 115200 baud, 8 data bits, even parity, 1 stop bit
PORT1_RS232_BEGIN(115200, SERIAL_8E1);
PORT2_RS232_BEGIN(115200, SERIAL_8E1);
PORT3_RS232_BEGIN(115200, SERIAL_8E1);
PORT4_RS232_BEGIN(115200, SERIAL_8E1);

// RS232 does not require beginTransmission()

// Use Serial1 and Serial2 to write to the ports
Serial1.write("Hello World 1\r\n");
Serial2.write("Hello World 2\r\n");
Serial3.write("Hello World 3\r\n");
Serial4.write("Hello World 4\r\n");

When using the P1AM Serial with a library that has its own begin() function, i.e. ArduinoModbus, manually configure the mode of the ports with serial_port_config() before calling the library's begin() function.

#include <ArduinoRS485.h>
#include <ArduinoModbus.h>
#include <P1AM_Serial.h>

ModbusRTUClientClass rtu_client(Port1); // Create modbus client on port 1

void setup() {

    serial_port_config(1, RS232_MODE); // Set port 1 to RS232 prior to starting modbus client

    rtu_client.begin(115200); // Start modbus client on port 1
}

Default Pin Usage

Pins	Port	Function
14	Port 1	TX
13	Port 1	RX
A6	Port 1	RS485 DE/RE
3	Port 1	RS232/RS485 Select
0	Port 2	TX
1	Port 2	RX
6	Port 2	RS485 DE/RE
2	Port 2	RS232/RS485 Select

Addtional Pin Usage

Pins	Port	Function
11	Port 3	TX
12	Port 3	RX
A1	Port 3	RS485 DE/RE
A0	Port 3	RS232/RS485 Select
4	Port 4	TX
5	Port 4	RX
A5	Port 4	RS485 DE/RE
A2	Port 4	RS232/RS485 Select