eZ80L92 MCU
Product Specification
139
2
I C Serial I/O Interface
General Characteristics
The I2C serial I/O bus is a two-wire communication interface that can operate in four
modes:
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•
•
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MASTER TRANSMIT
MASTER RECEIVE
SLAVE TRANSMIT
SLAVE RECEIVE
The I2C interface consists of the Serial Clock (SCL) and the Serial Data (SDA). Both SDA
and SCL are bidirectional lines, connected to a positive supply voltage via an external
pull-up resistor. When the bus is free, both lines are High. The output stages of devices
connected to the bus must be configured as open-drain outputs. Data on the I2C bus can be
transferred at a rate of up to 100 Kbps in STANDARD mode, or up to 400 Kbps in FAST
mode. One clock pulse is generated for each data bit transferred.
Clocking Overview
If another device on the I2C bus drives the clock line when the I2C is in MASTER mode,
the I2C synchronizes its clock to the I2C bus clock. The High period of the clock is
determined by the device that generates the shortest High clock period. The Low period of
the clock is determined by the device that generates the longest Low clock period.
A slave may stretch the Low period of the clock to slow down the bus master. The Low
period may also be stretched for handshaking purposes. This can be done after each bit
transfer or each byte transfer. The I2C stretches the clock after each byte transfer until the
IFLG bit in the I2C_CTL register is cleared.
Bus Arbitration Overview
In MASTER mode, the I2C checks that each transmitted logic 1 appears on the I2C bus as
a logic 1. If another device on the bus overrules and pulls the SDA signal Low, arbitration
is lost. If arbitration is lost during the transmission of a data byte or a Not-Acknowledge
bit, the I2C returns to the idle state. If arbitration is lost during the transmission of an
address, the I2C switches to SLAVE mode so that it can recognize its own slave address or
the general call address.
PS013015-0316
I2C Serial I/O Interface
ZILOG [ ZILOG, INC. ]
