PIC16LC65A-04E/SS 查看數據表（PDF） - Microchip Technology
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PIC16LC65A-04E/SS Datasheet PDF : 336 Pages
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Applicable Devices
61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67
PIC16C6X
11.4 I2C™ Overview
This section provides an overview of the Inter-Inte-
grated Circuit (I2C) bus, with Section 11.5 discussing
the operation of the SSP module in I2C mode.
The I2C bus is a two-wire serial interface developed by
the Philips® Corporation. The original specification, or
standard mode, was for data transfers of up to 100
Kbps. The enhanced specification (fast mode) is also
supported. This device will communicate with both
standard and fast mode devices if attached to the same
bus. The clock will determine the data rate.
The I2C interface employs a comprehensive protocol to
ensure reliable transmission and reception of data.
When transmitting data, one device is the “master”
which initiates transfer on the bus and generates the
clock signals to permit that transfer, while the other
device(s) acts as the “slave.” All portions of the slave
protocol are implemented in the SSP module’s hard-
ware, except general call support, while portions of the
master protocol need to be addressed in the
PIC16CXX software. Table 11-3 defines some of the
I2C bus terminology. For additional information on the
I2C interface specification, refer to the Philips docu-
ment “The I2C bus and how to use it.” #939839340011,
which can be obtained from the Philips Corporation.
In the I2C interface protocol each device has an
address. When a master wishes to initiate a data trans-
fer, it first transmits the address of the device that it
wishes to “talk” to. All devices “listen” to see if this is
their address. Within this address, a bit specifies if the
master wishes to read-from/write-to the slave device.
The master and slave are always in opposite modes
(transmitter/receiver) of operation during a data trans-
fer. That is they can be thought of as operating in either
of these two relations:
• Master-transmitter and Slave-receiver
• Slave-transmitter and Master-receiver
In both cases the master generates the clock signal.
The output stages of the clock (SCL) and data (SDA)
lines must have an open-drain or open-collector in
order to perform the wired-AND function of the bus.
External pull-up resistors are used to ensure a high
level when no device is pulling the line down. The num-
ber of devices that may be attached to the I2C bus is
limited only by the maximum bus loading specification
of 400 pF.
11.4.1 INITIATING AND TERMINATING DATA
TRANSFER
During times of no data transfer (idle time), both the
clock line (SCL) and the data line (SDA) are pulled high
through the external pull-up resistors. The START and
STOP conditions determine the start and stop of data
transmission. The START condition is defined as a high
to low transition of the SDA when the SCL is high. The
STOP condition is defined as a low to high transition of
the SDA when the SCL is high. Figure 11-14 shows the
START and STOP conditions. The master generates
these conditions for starting and terminating data trans-
fer. Due to the definition of the START and STOP con-
ditions, when data is being transmitted, the SDA line
can only change state when the SCL line is low.
FIGURE 11-14: START AND STOP
CONDITIONS
SDA
SCL S
Start
Change
Condition of Data
Allowed
P
Change Stop
of Data Condition
Allowed
TABLE 11-3: I2C BUS TERMINOLOGY
Term
Description
Transmitter
Receiver
Master
Slave
Multi-master
Arbitration
Synchronization
The device that sends the data to the bus.
The device that receives the data from the bus.
The device which initiates the transfer, generates the clock and terminates the transfer.
The device addressed by a master.
More than one master device in a system. These masters can attempt to control the bus at the
same time without corrupting the message.
Procedure that ensures that only one of the master devices will control the bus. This ensure that
the transfer data does not get corrupted.
Procedure where the clock signals of two or more devices are synchronized.
© 1997 Microchip Technology Inc.
DS30234D-page 95
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