Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-447
I2
C
COMMUNICATION
16
PROCESSOR
MODULE
16.13.1 Features
The following is a list of the I2C controller’s main features:
Two-Pin Interface
Full-Duplex Operation
Master or Slave I2C Mode Support
MultiMaster Environment Support
Continuous Transfer Mode for Autoscanning of a Peripheral
Supports Maximum Capacitive Load of 400PF on Both Bus Lines (Fully I
2C Compliant)
Independent Programmable Baud Rate Generator
Supports I2C Low and High Speed Operation
Supports 7-Bit I2C Addressing
Open-Drain Output Pins Support MultiMaster Configuration
Local Loopback Capability for Testing
16.13.2 I2C Controller Clocking and Pin Functions
Both the serial data (SDA) and serial clock (SCL) are bidirectional pins that need to be
connected to a positive 5V power supply via an external pull-up resistor in the 6.8K Ohm to
10K Ohm range. Both pins are high when the I2C bus is free. The SCL signal clocks in
received data and clocks out transmitted data on the SDA pin.
The I2C controller can be configured as a master or slave. When configured as a master, the
I2C controller generates SCL, and then initiates and terminates the I/O operation. In addition,
the I2C controller generates the SCL signal via a dedicated baud rate generator that takes
Clock. When configured as a slave, the I2C controller receives SCL as an input. An I2C transaction is initiated when the master generates a start condition, which is defined
as the SDA signal making a high-to-low transition while SCL is high. An acknowledge (ACK)
is generated by the I2C receiver after each byte transfer. The receiver signals an ACK by
driving the SDA signal low during the SCL clock pulse immediately following each data byte
transmission. The data and ACK signals are always sampled on the rising edge of SCL. If
the receiver does not issue an ACK after a data byte is transmitted, the I2C master generates
a stop condition and transmission stops. A stop condition is when the SDA signal makes a
low to high transition while the SCL signal remains high, as illustrated in
Figure 16-125.