M44C892
M44C892
M44C092
Rev. A5, 14-Dec-01
57 (84)
configurations, the SSI, in I2C mode is intended for use
purely as a master controller on a single master bus
system. So all reference to multiple bus control and bus
contention will be omitted at this point.
All data is packaged into 8-bit telegrams plus a trailing
handshaking
or
acknowledge-bit.
Normally
the
communication channel is opened with a so-called start
condition, which initializes all devices connected to the
bus. This is then followed by a data telegram, transmitted
by the master controller device. This telegram usually
contains an 8-bit address code to activate a single slave
device connected onto the I2C bus. Each slave receives
this address and compares it with it’s own unique address.
The addressed slave device, if ready to receive data will
respond by pulling the SD line low during the 9th clock
pulse. This represents a so-called I2C acknowledge. The
controller on detecting this affirmative acknowledge then
opens a connection to the required slave. Data can then be
passed back and forth by the master controller, each 8-bit
telegram being acknowledged by the respective recipient.
The communication is finally closed by the master device
and the slave device put back into standby by applying a
stop condition onto the bus.
(2)
(1)
(4)
(3)
(1)
Start
condition
Data
valid
Data
change
Data
valid
Stop
condition
13832
SC
SD
Figure 64. I2C bus protocol 1
Bus not busy (1)
Both data and clock lines remain HIGH.
Start data transfer (2)
A HIGH to LOW transition of the SD line while
the clock (SC) is HIGH defines a START
condition.
Stop data transfer (3)
A LOW to HIGH transition of the SD line while
the clock (SC) is HIGH defines a STOP condition.
Data valid (4)
The state of the data line represents valid data
when, after START condition, the data line is
stable for the duration of the HIGH period of the
clock signal.
Acknowledge
All address and data words are serially transmitted
to and from device in eight–bit words. The
receiving device returns a zero on the data line
during the ninth clock cycle to acknowledge word
receipt.
13833
SC
SD
Start
1n
89
1st Bit
8th Bit
ACK
Stop
Figure 65. I2C bus protocol 2