CAT9555 Datasheet, PDF (9/18 Pages) Catalyst Semiconductor – 16-bit I2C and SMBus I/O Port with Interrupt

CAT9555
FUNCTIONAL DESCRIPTION
The CAT9555 general purpose input/output (GPIO)
peripheral provides up to sixteen I/O ports, controlled
through an I²C compatible serial interface
The CAT9555 supports the I²C Bus data transmission
protocol. This Inter-Integrated Circuit Bus protocol
defines any device that sends data to the bus to be a
transmitter and any device receiving data to be a
receiver. The transfer is controlled by the Master
device which generates the serial clock and all
START and STOP conditions for bus access. The
CAT9555 operates as a Slave device. Both the
Master device and Slave device can operate as either
transmitter or receiver, but the Master device controls
which mode is activated.
I²C BUS PROTOCOL
The features of the I²C bus protocol are defined as
follows:
(1) Data transfer may be initiated only when the bus
is not busy.
(2) During a data transfer, the data line must remain
stable whenever the clock line is high. Any
changes in the data line while the clock line is
high will be interpreted as a START or STOP
condition (Figure 5).
START AND STOP CONDITIONS
The START Condition precedes all commands to the
device, and is defined as a HIGH to LOW transition of
SDA when SCL is HIGH. The CAT9555 monitors the
SDA and SCL lines and will not respond until this
condition is met.
A LOW to HIGH transition of SDA when SCL is HIGH
determines the STOP condition. All operations must
end with a STOP condition.
DEVICE ADDRESSING
After the bus Master sends a START condition, a
slave address byte is required to enable the CAT9555
for a read or write operation. The four most significant
bits of the slave address are fixed as binary 0100
(Figure 6). The CAT9555 uses the next three bits as
address bits.
The address bits A2, A1 and A0 are used to select
which device is accessed from maximum eight
devices on the same bus. These bits must compare to
their hardwired input pins. The 8th bit following the 7-
bit slave address is the R/¯W¯ bit that specifies whether
a read or write operation is to be performed. When
this bit is set to “1”, a read operation is initiated, and
when set to “0”, a write operation is selected.
Following the START condition and the slave address
byte, the CAT9555 monitors the bus and responds
with an acknowledge (on the SDA line) when its
address matches the transmitted slave address. The
CAT9555 then performs a read or a write operation
depending on the state of the R/¯W¯ bit.
SCL
SDA
© 2010 SCILLC. All rights reserved
Characteristics subject to change without notice
START
CONDITION
STOP
CONDITION
Figure 5. START/STOP Condition
SLAVE ADDRESS
0 1 0 0 A2 A1 A0 R/W
FIXED
PROGRAMMABLE
HARDWARE
SELECTABLE
Figure 6. CAT9555 Slave Address
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Doc. No. MD-9003, Rev. J