RS232/485 Half Duplex

Description

This feature, present ton OI-Core/OI-CoreLite allow you to use two different protocol on same physical interface: RS485 half duplex or RS232.

There is no terminaison resistance. If you use RS485 bus and place the module at end of line you will need to add a 120Ohms resistance.

Characteristics

RS232 specifications
Requirements	Type	Value
Driver output voltage (min)	±5V	loaded with 3kΩ to Ground
Receiver input voltage high	2.2V	above this value, a logic ‘1’ is guaranteed
Receiver input voltage low	0.8V	below this value, a logic ‘0 ‘ is guaranteed
Receiver maximum input voltage	25V
Receiver minimum input voltage	-25V

RS485 specifications
Requirements	Type	Value
Driver differential voltage (typical)	2V
Driver differential voltage (min)	1.5V
Driver differential voltage (max)	5V

Code examples

The example code above demonstrates how to use RS485 on OI-Core/OI-CoreLite.

#include "OpenIndus.h"
#include "Arduino.h"

OICore core;

void setup(void)
{
    Serial.begin(115200);
    
    /* Initialize RS485 */
    core.rs.begin(9600, RS::Config::_8N1, RS::Mode::RS485);
}

void loop(void)
{
    uint8_t data[64] = {0};
    size_t size = 0;
    
    size = core.rs.available(); // Get number of available bytes
    if (size) {
        core.rs.read(data, size); // Read available data
        Serial.printf("%s\n", data);
    }

    core.rs.write(data, size); // Echo back the received data

    delay(10);
}

To use RS232 instead of RS485, just change the mode in the begin function:

core.rs.begin(9600, RS::Config::_8N1, RS::Mode::RS232);

Software API

class RS

RS485/232 bus class.

Public Types

enum Mode

RS communication mode.

Values:

enumerator RS485

enumerator RS232

enum Config

RS communication configuration Format: [Data bits] + [Parity] + [Stop bits] Parity: N=None, E=Even, O=Odd Exemple: 8N1 = 8 data bits, No parity, 1 stop bit.

Values:

enumerator _8N1

enumerator _8E1

enumerator _8O1

enumerator _7N1

enumerator _7E1

enumerator _7O1

Public Functions

inline RS(spi_host_device_t host, gpio_num_t cs, gpio_num_t intr)

Constructor.

Parameters:

host – SPI host device
cs – Chip select pin
intr – Interrupt pin

inline ~RS(): Destructor.

void begin(uint32_t baudrate = 115200, Config config = _8N1, Mode mode = RS485)

Initializes RS communication.

Parameters:

baudrate – in bits per second (baud)
config – 8N1 by default
mode – RS485 or RS232

void end(void): Disables RS communication.

int available(void)

Get the number of bytes available for reading from the serial buffer.

Returns:: The number of bytes available to read.

int read(void)

Reads incoming serial data.

Returns:: The first byte of incoming serial data available (or -1 if no data is available)

size_t read(uint8_t *buffer, size_t size)

Reads bytes from the serial port into a buffer.

Parameters:

buffer – the buffer to store the bytes in. Allowed data types: array of char or byte.
size – the number of bytes to read. Allowed data types: int.

Returns:

The number of bytes placed in the buffer.

size_t write(uint8_t byte)

Writes binary data to the serial port.

Parameters:: byte – byte to send
Returns:: The number of bytes written.

size_t write(const uint8_t *buffer, size_t size)

Writes binary data to the serial port.

Parameters:

buffer – an array to send as a series of bytes.
size – the number of bytes to be sent from the array.

Returns:

The number of bytes written.