CAT24WC257
IftheMastertransmitsmorethan64bytesbeforesending
the STOP condition, the address counter ‘wraps around’,
and previously transmitted data will be overwritten.
terminates data transmission and waits for a STOP
condition.
WRITE OPERATIONS
When all 64 bytes are received, and the STOP condition
has been sent by the Master, the internal programming
cycle begins. At this point, all received data is written to
the CAT24WC257 in a single write cycle.
Byte Write
In the Byte Write mode, the Master device sends the
START condition and the slave address information
(with the R/W bit set to zero) to the Slave device. After
the Slave generates an acknowledge, the Master sends
two 8-bit address words that are to be written into the
address pointers of the CAT24WC257. After receiving
another acknowledge from the Slave, the Master device
transmits the data to be written into the addressed
memory location. The CAT24WC257 acknowledges
once more and the Master generates the STOP condi-
tion. At this time, the device begins an internal program-
ming cycle to nonvolatile memory. While the cycle is in
progress, thedevicewillnotrespondtoanyrequestfrom
the Master device.
Acknowledge Polling
Disabling of the inputs 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,
CAT24WC257 initiates the internal write cycle. ACK
polling can be initiated immediately. This involves issu-
ing the start condition followed by the slave address for
a write operation. If CAT24WC257 is still busy with the
write operation, no ACK will be returned. If
CAT24WC257 has completed the write operation, an
ACK will be returned and the host can then proceed with
the next read or write operation.
Page Write
The CAT24WC257 writes up to 64 bytes of data, in a
single write cycle, using the Page Write operation. The
page write operation is initiated in the same manner as
the byte write operation, however instead of terminating
after the initial byte is transmitted, the Master is allowed
to send up to 63 additional bytes. After each byte has
been transmitted, CAT24WC257 will respond with an
acknowledge, and internally increment the six low order
address bits by one. The high order bits remain un-
changed.
WRITE PROTECTION
The Write Protection feature allows the user to protect
against inadvertent programming of the memory array.
If the WP pin is tied to VCC, the top 1/4 array of memory
(locations 6000H to 7FFFH) is protected and becomes
read only. The CAT24WC257 will accept both slave and
byte addresses, but the memory location accessed is
protected from programming by the device’s failure to
send an acknowledge after the first byte of data is
received.
Figure 6. Byte Write Timing
S
T
A
R
T
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
BYTE ADDRESS
–A A –A
0
A
DATA
15
8
7
SDA LINE
S
P
X X
A
C
K
A
C
K
A
C
K
A
C
K
=Don't Care Bit
*
Figure 7. Page Write Timing
S
T
A
R
T
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
BYTE ADDRESS
–A A –A
0
A
DATA
DATA n
DATA n+63
15
8
7
SDA LINE
S
P
*
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
=Don't Care Bit
*
Doc. No. 1030, Rev. E
6
CATALYST [ CATALYST SEMICONDUCTOR ]
