CAT24WC128
Preliminary
I2C BUS PROTOCOL
PIN DESCRIPTIONS
The features of the I2C bus protocol are defined as
follows:
SCL: Serial Clock
The serial clock input clocks all data transferred into or
out of the device.
(1) Data transfer may be initiated only when the bus
is not busy.
SDA: Serial Data/Address
The bidirectional serial data/address pin is used to
transfer all data into and out of the device. The SDA pin
is an open drain output and can be wire-ORed with
other open drain or open collector outputs.
(2) During a data transfer, the data line must remain
stablewhenevertheclocklineishigh.Anychanges
in the data line while the clock line is high will be
interpreted as a START or STOP condition.
WP: Write Protect
START Condition
This input, when tied to GND, allows write operations to
the entire memory. When this pin is tied to Vcc, the
entire memory is write protected. When left floating,
memory is unprotected.
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 CAT24WC128 monitors
the SDA and SCL lines and will not respond until this
condition is met.
STOP Condition
A LOW to HIGH transition of SDA when SCL is HIGH
determines the STOP condition. All operations must
end with a STOP condition.
Figure 1. Bus Timing
t
t
t
F
HIGH
R
t
t
LOW
LOW
SCL
t
t
HD:DAT
SU:STA
t
t
t
t
HD:STA
SU:DAT
SU:STO
SDA IN
BUF
t
t
DH
AA
SDA OUT
5020 FHD F03
Figure 2. Write Cycle Timing
SCL
SDA
8TH BIT
BYTE n
ACK
t
WR
STOP
CONDITION
START
CONDITION
ADDRESS
5020 FHD F04
Figure 3. Start/Stop Timing
SDA
SCL
START BIT
STOP BIT
5020 FHD F05
Doc. No. 25060-00 6/99 S-1
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