I2C

Sends and receives serial data using I²C synchronous communication.

• U3: Requires U3 hardware version 1.21+.

• NumI2CWordsSend: This is the number of I²C bytes to send divided by 2. If the number of bytes is odd, round up and add an extra zero to the packet. This parameter is actually just to specify the size of this packet, as the NumI2CbytesToSend parameter below actually specifies how many bytes will be sent.

• I2COptions: If ResetAtStart is true, an I²C bus reset will be done before communicating.

• SpeedAdjust: Allows the communication frequency to be reduced. 0 is the maximum speed of ~150kHz. 20 is a speed of ~70 kHz. 255 is the minimum speed of ~10 kHz.

• SDAP/SCLP -PinNum: Assigns which digital I/O line is used for each I²C line. Value passed is 0-19 corresponding to the normal digital I/O numbers as specified in the Digital I/O section of your device datasheet (U3/U6/UE9). Note that the screw terminals labeled “SDA” and “SCL” on hardware revision 1.20 or 1.21 are not used for I²C. Note that the I²C bus generally requires pull-up resistors of perhaps 4.7 kΩ from SDA to Vs and SCL to Vs.

• AddressByte: This is the first byte of data sent on the I²C bus. The upper 7 bits are the address of the slave chip and bit 0 is the read/write bit. Note that the read/write bit is controlled automatically by the LabJack, and thus bit 0 is ignored.

• NumI2CBytesToSend: Specifies how many I²C bytes will be sent (valid values are 0-50 on the U3/U6 and 0-240 on the UE9).

• NumI2CBytesToReceive: Specifies how many I²C bytes will be read (valid values are 0-52 on the U3/U6 and 0-240 on the UE9).

• I2Cbyte#: In the command, these are the bytes to send. In the response, these are the bytes read.

• NumI2CWordsReceive: This is the number of I²C bytes to receive divided by 2. If the number of bytes is odd, the value is rounded up and an extra zero is added to the packet. This parameter is actually just to specify the size of this packet, as the NumI2CbytesToReceive parameter above actually specifies how many bytes to read.

• AckArray#: Represents a 32-bit value where bits are set if the corresponding I²C write byte was ACKed. Useful for debugging up to the first 32 write bytes of communication. Bit 0 corresponds to the last data byte, bit 1 corresponds to the second to last data byte, and so on up to the address byte. So if n is the number of data bytes, the ACK value should be (2^(n+1))-1.