Data Sheet

10. I²C command encoding

As described in Section 8, the Tic’s I²C commands each use one of four formats: quick, 7-bit write,

32-bit write, and block read. This section explains how these four command formats are encoded as

sequences of bytes within I²C transfers.

For a reference implementation of this protocol, see the TicI2C class in our Tic Stepper Motor

Controller library for Arduino [https://github.com/pololu/tic-arduino].

Note that most of these formats are compatible with the SMBus protocols of the same names; an

exception is the block read command, although an SMBus-compatible workaround can be found in its

description below.

The default slave address for the Tic is 0001110b (0x0E in hex; 14 in decimal), but this is a setting

(“device number”) you can change. (This setting also determines the Tic’s device number when using

the Pololu protocol over TTL serial.)

As specified by the I²C standard, a transfer’s address byte consists of the 7-bit slave address followed

by another bit to indicate the transfer direction: 0 for writing to the slave, 1 for reading from the

slave. This is denoted by “addr + Wr” and “addr + Rd” below. With the Tic’s default slave address, the

address byte is 00011100b (0x1C) for a write transfer and 00011101b (0x1D) for a read transfer.

These symbols are also used in the format descriptions below:

• S: start condition

• P: stop condition

• A: acknowledge (ACK)

• N: not acknowledge (NACK)

Any stop condition followed by a start condition can optionally be replaced with a repeated start

condition.

Quick

master: S addr + Wr command P

Tic: A A

A Quick command sends no data and simply consists of the command byte.

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