This page documents the Wire library for the I2C protocol. You can use this library in the Maple IDE by choosing the Wire item under the Sketch > Import Library... menu.

If you are using the Unix toolchain, the library is located in the /libraries/Wire/ libmaple directory.

Wire Function Reference

Joins the i2c bus as master, using pin 20 as SDA and pin 21 as SCL (this is compatible with the pin settings on the Arduino Mega).
Wire.begin(sda, scl)
Like Wire.begin(), but with the given pins as SDA and SCL.
Set up a transmission to a slave device with the given (7-bit) address. Bytes subsequently queued for transmission (using Wire.send) will be sent to slave_address when void Wire.endTransmission() is called.
void Wire.send(byte)
Queues the given byte (uint8 or int) to the slave address previously specified by a call to Wire.beginTransmission. At most 32 bytes may be queued in a single transmission.
Queues a given string (char*) for transmission. The characters of the string are individually queued for transmission as bytes. At most 32 bytes may be queued in a single transmission.
Wire.send(buffer, length)
Queues a byte buffer buffer (uint8* or int*), with length elements, for transmission. At most 32 bytes may be queued in a single transmission.

Ends a transmission (begun by Wire.beginTransmission(uint8)), and actually sends the bytes queued by calls to Wire.send.

The return value is one of the following status codes:

  • SUCCESS: All bytes were transmitted successfully.
  • EDATA: More than 32 bytes were queued for transmission. No bytes are actually sent when this happens.
  • ENACKADDR: Did not receive ACK on transmit of address. No bytes are actually sent when this happens.
  • ENACKTRNS: Did not receive ACK during transmit of data. Some bytes may have been sent when this happens; however, the transmission is aborted after the first byte of data which is not ACKed by the slave device.
  • EOTHER: Other error occurred.
Wire.requestFrom(address, num_bytes)

Requests num_bytes bytes from 7-bit slave address address. Returns the actual number of bytes read. These bytes may subsequently be read one at a time using Wire.receive().

Note: if num_bytes exceeds the size of the transmit/receive buffer (currently 32), it will be truncated to 32.

Get and return the next byte read during the previous call to Wire.requestFrom(uint8, int). You can check how many bytes are left to read using uint8 Wire.available().
Returns the number of bytes which are still available for reading (with Wire.receive()) from the last call to Wire.requestFrom(uint8, int).

Arduino Compatibility

This implementation is synchronous, and thus supports only a subset of the full Wire interface (however, the functionality which is supported is fully compatible with Arduino). For now, please use the function reference which follows when developing projects using our implementation.

Please note that the current implementation only supports master mode using a bit-banged (software) protocol. For now, use of the hardware I2C peripheral is only available through i2c.h.