STE2002_06 Datasheet, PDF (25/61 Pages) STMicroelectronics – 81 x 128 single-chip LCD controller/driver

STE2002
Bus interfaces
By definition, a device that gives out a message is called "transmitter", the receiving device
that gets the signals is called "receiver". The device that controls the message is called
"master". The devices that are controlled by the master are called "slaves"
Acknowledge. Each byte of eight bits is followed by one acknowledge bit. This
acknowledge bit is a low level put on the bus by the receiver, whereas the master generates
an extra acknowledge related clock pulse.
A slave receiver which is addressed must generate an acknowledge after the reception of
each byte. Also, a master receiver must generate an acknowledge after the reception of
each byte that has been clocked out of the slave transmitter. The device that acknowledges
has to pull down the SDA_IN line during the acknowledge clock pulse. Of course, setup and
hold time must be taken into account. A master receiver must signal an end-of-data to the
slave transmitter by not generating an acknowledge on the last byte that has been clocked
out of the slave. In this case, the transmitter must leave the data line High to enable the
master to generate the STOP condition.
Connecting SDA_IN and SDA_OUT together the SDA line become the standard data line.
Having the acknowledge output (SDAOUT) separated from the serial data line is
advantageous in Chip-On-Glass (COG) applications. In COG applications where the track
resistance from the SDAOUT pad to the system SDA line can be significant, a potential
divider is generated by the bus pull-up resistor and the Indium Tin Oxide (ITO) track
resistance. It is possible that during the acknowledge cycle the STE2002 will not be able to
create a valid logic 0 level. By splitting the SDA input from the output the device could be
used in a mode that ignores the acknowledge bit. In COG applications where the
acknowledge cycle is required, it is necessary to minimize the track resistance from the
SDACK pad to the system SDA line to guarantee a valid LOW level.
To be compliant with the I²C-bus Hs-mode specification the STE2002 is able to detect the
special sequence "S00001xxx". After this sequence no acknowledge pulse is generated.
Since no internal modification are applied to work in Hs-mode, the device is able to work in
Hs-mode without detecting the master code.
Figure 28. Bit transfer and START,STOP conditions definition
CLOCK
DATA LINE
STABLE
DATA VALID
DATA
START
CONDITION
CHANGE OF
DATA ALLOWED
D00IN1151
STOP
CONDITION
Figure 29. Acknowledgment on the I²C-bus
START
SCLK FROM
MASTER
1
2
DATA OUTPUT
BY TRANSMITTER
DATA OUTPUT
BY RECEIVER
MSB
D00IN1152
CLOCK PULSE FOR
ACKNOWLEDGEMENT
8
9
LSB
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