I2C Communications (Wire)

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This is an I²C communications library that facilitates two-wire class communications with I²C/TWI devices (also called "Wire Library"). The pull-up to communication lines are needed. With a total of 8 serial channels available. You cannot use slave device. The followings describe channels corresponding to pins and can confirmed using the pin map. To use, specify #include <wire.h>.

Wire: A5(SCL), A4(SDA)
Wire1: 0(SCL), 1(SDA)
Wire2: 7(SCL), 6(SDA)
Wire3: 26(SCL), 24(SDA)
Wire4: 5(SCL), 3(SDA)
Wire5: 8(SCL), 9(SDA)
Wire6: 11(SCL), 12(SDA)
Wire7: 60(SCL), 58(SDA)

begin

Description

Initiates the Wire library.

Syntax

Wire.begin()

Parameters

None

Returns

None

requestFrom

Description

Used by the master to request bytes from a slave device. The bytes may then be retrieved with the available() and read() functions.

Syntax

Wire.requestFrom(address, quantity)
Wire.requestFrom(address, quantity, stop)

Parameters

address: The 7-bit address of the device from which to request bytes.
quantity: The number of bytes to request.
stop: Boolean. True will send a stop message after the request, releasing the bus. False will continually send a restart after the request, keeping the connection active.

Returns

byte: The number of bytes returned from the slave device.

beginTransmission

Description

Begin a transmission to the I²C slave device with the given address. Subsequently, queue bytes for transmission with the write() function and transmit them by calling endTransmission().

Syntax

Wire.beginTransmission(unsigned char address)

Parameters

address: The 7-bit address of the device to which to transmit

Returns

None

endTransmission

Description

Ends a transmission to a slave device that was begun by beginTransmission() and transmits the bytes that were queued by write().

Syntax

unsigned char Wire.endTransmission()

Parameters

None

Returns

0: Success
1: Data too long to fit in transmit buffer
2: Received NACK on transmit of address
3: Received NACK on transmit of data
4: Other error

write

Description

Adds a character string or data to the end of the transmit buffer.

Syntax

Wire.write(value)
Wire.write(string)
Wire.write(data, length)

Parameters

value: A value to send as a single byte
string: A string to send as a series of bytes
data: An array of data to send as bytes
length: The number of bytes to transmit

Returns

byte: Write() will return the number of bytes written, though reading that number is optional.

available

Description

Returns the number of bytes available for retrieval in the receive buffer.

Syntax

Wire.available()

Parameters

None

Returns

The number of bytes available for reading.

read

Description

Reads one byte of data from the receive buffer.

Syntax

Wire.read()

Parameters

None

Returns

The next byte received.

---

Receive data from slave device #2.

#include <Arduino.h>
#include <Wire.h>
void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output
}
 
void loop()
{
  Wire.requestFrom(2, 6);    // request 6 bytes from slave device #2
 
  while(Wire.available())    // slave may send less than requested
  { 
    char c = Wire.read();    // receive a byte as character
    Serial.print(c);         // print the character
  }
 
  delay(500);
}