32-2
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
The I
2
C receiver and transmitter are double-buffered, which corresponds to an effective
two-character FIFO latency. In normal operation, the msb (bit 0) is shifted out Þrst. When
the I
2
C is not enabled in the I
2
C mode register (I2MOD[EN] = 0), it consumes little power.
32.1 I
2
C Features
The following is a list of the I
2
C controllerÕs main features:
¥
Two-signal interface (SDA on PB[27] and SCL on PB[26])
¥
Support for master and slave I
2
C operation
¥
Multiple-master environment support
¥
Continuous transfer mode for autoscanning of a peripheral
¥
Supports a maximum clock rate of 520 KHz (with a CPM utilization of 25%),
assuming a 25-MHz system clock.
¥
Independent, programmable baud-rate generator
¥
Supports 7-bit I
2
C addressing
¥
Open-drain output signals allow multiple master conÞguration
¥
Local loopback capability for testing
32.2 I
2
C Controller Clocking and Signal Functions
The I
2
C controller can be conÞgured as a master or slave for the serial channel. As a master,
the controllerÕs BRG provides the transfer clock. The I
2
C BRG takes its input from the BRG
clock (BRGCLK), which is described in Section 15.3, ÒClock Signals.Ó
SDA and SCL are bidirectional signals connected to a positive supply voltage through an
external pull-up resistor. When the bus is free, both signals are pulled high. The general I
2
C
master/slave conÞguration is shown in Figure 32-2.
Figure 32-2. I
2
C Master/Slave General Configuration
When the I
2
C controller is the master, the SCL clock output, taken directly from the I
2
C
BRG, shifts receive data in and transmit data out through SDA. The transmitter arbitrates
VDD
VDD
Master
Slave
(EEPROM, for example)
SCL
SCL
SDA
SDA
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