pca9655e ON Semiconductor, pca9655e Datasheet - Page 15

• Manufacturer Part Number: pca9655e
• Description: Pca9655e Remote 16-bit I/o Expander For I2c Bus With Interrupt
• Manufacturer: ON Semiconductor

START and STOP Conditions
not busy. A START condition (S) occurs when there is a
HIGH−to−LOW transition of the data line while the clock is
System Configuration
receiving is the ‘receiver’. The device that controls the
Acknowledge
and the STOP conditions from transmitter to receiver is not
limited. Each 8−bit byte is followed by one acknowledge bit.
The acknowledge bit is a HIGH level put on the bus by the
transmitter, whereas the master generates an extra clock
pulse for the acknowledge bit.
acknowledge after the reception of each byte. Also, a master
must generate an acknowledge after the reception of each
byte that has been clocked out of the slave transmitter. The
Both data and clock lines remain HIGH when the bus is
A device generating a message is a ‘transmitter’; a device
The number of data bytes transferred between the START
A slave receiver which is addressed must generate an
SDA
SCL
SDA
SCL
TRANSMITTER/
RECEIVER
MASTER
SDA
SCL
START condition
S
Figure 13. Definition of START and STOP Conditions
RECEIVER
SLAVE
data valid
data line
stable;
Figure 14. System Configuration
TRANSMITTER/
Figure 12. Bit Transfer
RECEIVER
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SLAVE
allowed
change
of data
15
HIGH. A STOP condition (P) occurs when there is a
LOW−to−HIGH transition of the data line while the clock is
HIGH (see Figure 13).
message is the ‘master’ and the devices which are controlled
by the master are the ‘slaves’ (see Figure 14).
device that acknowledges has to pull down the SDA line
during the acknowledge clock pulse, such that the SDA line
is stable LOW during the HIGH period of the acknowledge
clock pulse; set−up time and hold time must be taken into
account.
by not generating an acknowledge on the last byte that has
been clocked out of the slave. In this event, the transmitter
must leave the data line HIGH to enable the master to
generate a STOP condition.
TRANSMITTER
A master receiver signals an end of data to the transmitter
MASTER
TRANSMITTER/
RECEIVER
MASTER
STOP condition
SLAVE
P
MULTIPLEXER
I
2
C−BUS
SDA
SCL