Datasheet

Device Address
0
Slave Address
0 1 1 A2 A1 A0
R/W
Fixed Programmable
Control Register and Command Byte
0 0 0 0 B1 B000
PCA9557
www.ti.com .................................................................................................................................................... SCPS133I – DECEMBER 2005 – REVISED JUNE 2008
The address of the PCA9557 is shown in Figure 4 .
Figure 4. PCA9557 Address
Address Reference
INPUTS
I
2
C BUS SLAVE ADDRESS
A2 A1 A0
L L L 24 (decimal), 18 (hexadecimal)
L L H 25 (decimal), 19 (hexadecimal)
L H L 26 (decimal), 1A (hexadecimal)
L H H 27 (decimal), 1B (hexadecimal)
H L L 28 (decimal), 1C (hexadecimal)
H L H 29 (decimal), 1D (hexadecimal)
H H L 30 (decimal), 1E (hexadecimal)
H H H 31 (decimal), 1F (hexadecimal)
The last bit of the slave address defines the operation (read or write) to be performed. A high (1) selects a read
operation, while a low (0) selects a write operation.
Following the successful acknowledgment of the address byte, the bus master sends a command byte that is
stored in the control register in the PCA9557. Two bits of this data byte state the operation (read or write) and
the internal registers (input, output, polarity inversion or configuration) that will be affected. This register can be
written or read through the I
2
C bus. The command byte is sent only during a write transmission.
Once a new command byte has been sent, the register that was addressed continues to be accessed by reads
until a new command byte has been sent.
Figure 5. Control Register Bits
Command Byte
CONTROL REGISTER BITS
COMMAND BYTE POWER-UP
REGISTER PROTOCOL
(HEX) DEFAULT
B1 B0
0 0 0x00 Input Port Read byte xxxx xxxx
0 1 0x01 Output Port Read/write byte 0000 0000
1 0 0x02 Polarity Inversion Read/write byte 1111 0000
1 1 0x03 Configuration Read/write byte 1111 1111
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