CAT24C01, CAT24C02, CAT24C04, CAT24C08, CAT24C16
http://onsemi.com
6
WRITE OPERATIONS
Byte Write
In Byte Write mode, the Master sends the START
condition and the Slave address with the R/W bit set to zero
to the Slave. After the Slave generates an acknowledge, the
Master sends the byte address that is to be written into the
address pointer of the CAT24Cxx. After receiving another
acknowledge from the Slave, the Master transmits the data
byte to be written into the addressed memory location. The
CAT24Cxx device will acknowledge the data byte and the
Master generates the STOP condition, at which time the
device begins its internal Write cycle to nonvolatile memory
(Figure 6). While this internal cycle is in progress (t
WR
), the
SDA output will be tri
−
stated and the CAT24Cxx will not
respond to any request from the Master device (Figure 7).
Page Write
The CAT24Cxx writes up to 16 bytes of data in a single
write cycle, using the Page Write operation (Figure 8). The
Page Write operation is initiated in the same manner as the
Byte Write operation, however instead of terminating after
the data byte is transmitted, the Master is allowed to send up
to fifteen additional bytes. After each byte has been
transmitted the CAT24Cxx will respond with an
acknowledge and internally increments the four low order
address bits. The high order bits that define the page address
remain unchanged. If the Master transmits more than sixteen
bytes prior to sending the STOP condition, the address
counter ‘wraps around’ to the beginning of page and
previously transmitted data will be overwritten. Once all
sixteen bytes are received and the STOP condition has been
sent by the Master, the internal Write cycle begins. At this
point all received data is written to the CAT24Cxx in a single
write cycle.
Acknowledge Polling
The acknowledge (ACK) polling routine can be used to
take advantage of the typical write cycle time. Once the stop
condition is issued to indicate the end of the host’s write
operation, the CAT24Cxx initiates the internal write cycle.
The ACK polling can be initiated immediately. This
involves issuing the start condition followed by the slave
address for a write operation. If the CAT24Cxx is still busy
with the write operation, NoACK will be returned. If the
CAT24Cxx has completed the internal write operation, an
ACK will be returned and the host can then proceed with the
next read or write operation.
Hardware Write Protection
With the WP pin held HIGH, the entire memory is
protected against Write operations. If the WP pin is left
floating or is grounded, it has no impact on the operation of
the CAT24Cxx. The state of the WP pin is strobed on the last
falling edge of SCL immediately preceding the first data
byte (Figure 9). If the WP pin is HIGH during the strobe
interval, the CAT24Cxx will not acknowledge the data byte
and the Write request will be rejected.
Delivery State
The CAT24Cxx is shipped erased, i.e., all bytes are FFh.
ADDRESS
BYTE
DATA
BYTE
SLAVE
ADDRESS
S
A
C
K
A
C
K
A
C
K
S
T
O
P
P
S
T
A
R
T
BUS ACTIVITY:
MASTER
SLAVE
* For the CAT24C01 a
7
= 0
a
7
−
a
0
d
7
−
d
0
Figure 6. Byte Write Sequence
