Figure 9-2. I 2 C Bus Protocol; Theory Of Operation - Sharp LH79524 User Manual

2
I C Module

9.1 Theory of Operation

The LH79524/LH79525 implements a two-wire I
Master or Slave mode. The block conforms to the I
rates up to 400 kbps. The two wires (pins) in the interface are SCL (serial clock) and
SDA (serial data).
2
The I C Module buffers a single byte of serial data on receive and transmit. Registers pro-
vide control over operating mode, serial clock frequency, and slave-mode address. A sta-
tus register contains status bits that remain set until cleared by software.
The slaves each have a unique address that is determined by the system designer. When
the master wants to communicate with a slave, the master transmits a start condition that
is then followed by the slave's address and a control bit (R/W) to determine if the master
wants to transmit data or receive data from the slave. The slave will then send an acknowl-
edge (ACK) pulse after the address and R/W bit is received to notify the master that the
slave has received the request. If the master (master-transmitter) is writing to the slave,
(slave-receiver), the receiver will receive a byte of data. This transaction will continue until
the master terminates the transmission with a stop condition. If the master (master-
receiver), is reading from the slave (slave-transmitter), the receiver will transmit a byte of
data to the master, and the master will then acknowledge the transaction with the ACK
pulse. This transaction will continue until the master terminates the transmission by not
acknowledging the transaction after the last byte is received, and then the master will issue
a stop condition. This is shown in Figure 9-2.
SDA
SCL
START OR
REPEATED
START
CONDITION
9-2
MSB
1 2 7
BYTE COMPLETE
INTERUPT WITHIN
Figure 9-2. I
Version 1.0
LH79524/LH79525 User's Guide
2
C Module capable of operating in either
2
C 2.1 Bus Specification for data
LSB ACK
(FROM SLAVE)
8 9 1
SCL HELD LOW
WHILE SERVICING
SLAVE INTERUPTS
2
C Bus Protocol
P
ACK
SR
(FROM RECEIVER)
2 3-8 9
STOP OR
REPEATED START
CONDITION
LH79525-68