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I2C (Wire)
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Utility
I2C Communications (Wire)
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 is needed. There is a total of eight serial channels available. You cannot use a slave device. The following information describes channels corresponding to pins, which can be confirmed by referring to 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.
Sample Program
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);
}