EZ80F91MCU Datasheet, PDF (238/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
219
I²C Serial I/O Interface
I²C General Characteristics
The Inter-Integrated Circuit (I²C) serial I/O bus is a two-wire communication inter-
face that can operate in four modes:
• MASTER TRANSMIT
• MASTER RECEIVE
• SLAVE TRANSMIT
• SLAVE RECEIVE
The I²C interface consists of a Serial Clock (SCL) and Serial Data (SDA). Both
SCL and SDA 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 long-
est Low clock period.
A slave can stretch the Low period of the clock to slow down the bus master. The
Low period can also be stretched for handshaking purposes. This result can be
accomplished 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
to 0.
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 sig-
nal Low, arbitration is lost. If arbitration is lost during the transmission of a data
byte or a Not Acknowledge (NACK) bit, the I²C returns to an idle state. If arbitra-
tion 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.
PS019209-0504
PRELIMINARY
I²C Serial I/O Interface