Data Sheet

ISM14585-L35 Specification
DOC-DS-14585-201807-3.0
Confidential Inventek Systems
Page 39
Figure 17 START BYTE Transfer
The START BYTE procedure is as follows:
1. Master generates a START condition.
2. Master transmits the START byte (0000 0001).
3. Master transmits the ACK clock pulse. (Present only to conform with the byte
handling format used on the bus)
4. No slave sets the ACK signal to 0.
5. Master generates a RESTART (R) condition.
A hardware receiver does not respond to the START BYTE because it is a reserved
address and resets after the RESTART condition is generated.
9.7.4 MULTIPLE MASTER ARBITRATION
The I2C Controller bus protocol allows multiple masters to reside on the same bus. If
there are two masters on the same I2C-bus, there is an arbitration procedure if both try
to take control of the bus at the same time by generating a START condition at the
same time. Once a master (for example, a microcontroller) has control of the bus, no
other master can take control until the first master sends a STOP condition and places
the bus in an idle state.
Arbitration takes place on the SDA line, while the SCL line is 1. The master, which
transmits a 1 while the other master transmits 0, loses arbitration and turns off its data
output stage. The master that lost arbitration can continue to generate clocks until the
end of the byte transfer. If both masters are addressing the same slave device, the
arbitration could go into the data phase. Figure 18 illustrates the timing of when two
masters are arbitrating on the bus.