Datasheet
See Figure 6 for a read example using the repeated
start condition to specify the starting memory location.
Reading Multiple Bytes from a Slave: The read oper-
ation can be used to read multiple bytes with a single
transfer. When reading bytes from the slave, the master
simply ACKs the data byte if it desires to read another
byte before terminating the transaction. After the mas-
ter reads the last byte, it must NACK to indicate the end
of the transfer and generate a stop condition.
Applications Information
Power Supply Decoupling
To achieve best results, it is highly recommended that a
decoupling capacitor is used on the IC power-supply
pins. Typical values of decoupling capacitors are 0.01µF
and 0.1µF. Use a high-quality, ceramic, surface-mount
capacitor, and mount it as close as possible to the V
CC
and GND pins of the IC to minimize lead inductance.
DS4550
I
2
C and JTAG Nonvolatile 9-Bit I/O
Expander Plus Memory
____________________________________________________________________ 17
Figure 6. I
2
C Communication Examples
SLAVE
ADDRESS*
START
START
1 0 1 0 A2 A1 A0 R/W
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
MSB LSB MSB LSB MSB LSB
b7 b6 b5 b4 b3 b2 b1 b0
READ/
WRITE
REGISTER ADDRESS
b7 b6 b5 b4 b3 b2 b1 b0
DATA
STOP
SINGLE BYTE WRITE
-WRITE I/O CONTROL 0
REGISTER TO 00h
SINGLE BYTE WRITE
-WRITE PULLUP ENABLE 0
REGISTER TO FFh
SINGLE BYTE READ
-READ I/O STATUS 0 RESISTER
TWO BYTE WRITE
-WRITE I/O CONTROL 0 AND
I/O CONTROL 1 REGISTERS TO 00h
START
STOP
1 0100000
11110 010
A0h F2h
START
REPEATED
START
A1h
MASTER
NACK
STOP
1 0100000
11111 000
F8h
10100 001
1 0100000
11110 010
A0h F2h
STOP
I/O STATUS
START
1 0100000 11110000
A0h F0h
STOP
DATA
FFh
00h 00h
EXAMPLE I
2
C TRANSACTIONS (WHEN A0, A1, AND A2 ARE CONNECTED TO GND)
TYPICAL I
2
C WRITE TRANSACTION
*THE SLAVE ADDRESS IS DETERMINED BY ADDRESS PINS A0, A1, AND A2.
00000 000
1
1111111
A0h
00000000
TWO BYTE READ
-READ I/O STATUS 0 AND I/O
STATUS 1 RGISTERS
A)
C)
B)
D)
D)
START
STOP
101000 00
111 11000
A0h F8h
A1h
1010 0001
I/O STATUS 0
DATA
I/O STATUS 1
DATA
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
MASTER
ACK
MASTER
NACK
REPEATED
START
00000000