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NM24C08U
Fairchild
Fairchild Semiconductor Fairchild
NM24C08U Datasheet PDF : 13 Pages
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Write Operations
BYTE WRITE
For a write operation a second address field is required which is
a word address that is comprised of eight bits and provides access
to any one of the 256 bytes in the selected page of memory. Upon
receipt of the byte address the NM24C08U/09U responds with an
acknowledge and waits for the next eight bits of data, again,
responding with an acknowledge. The master then terminates the
transfer by generating a stop condition, at which time the
NM24C08U/09U begins the internal write cycle to the nonvolatile
memory. While the internal write cycle is in progress the
NM24C08U/09U inputs are disabled, and the device will not
respond to any requests from the master. Refer to Figure 6 for the
address, acknowledge and data transfer sequence.
PAGE WRITE
The NM24C08U/09U is capable of a sixteen byte page write
operation. It is initiated in the same manner as the byte write
operation; but instead of terminating the write cycle after the first
data byte is transferred, the master can transmit up to fifteen more
bytes. After the receipt of each byte, the NM24C08U/09U will
respond with an acknowledge.
After the receipt of each byte, the internal address counter
increments to the next address and the next SDA data is accepted.
If the master should transmit more than sixteen bytes prior to
generating the stop condition, the address counter will "roll over"
and the previously written data will be overwritten. As with the byte
write operation, all inputs are disabled until completion of the
internal write cycle. Refer to Figure 7 for the address, acknowl-
edge, and data transfer sequence.
Acknowledge Polling
Once the stop condition is issued to indicate the end of the hosts
write operation the NM24C08U/09U initiates the internal write
cycle. ACK polling can be initiated immediately. This involves
issuing the start condition followed by the slave address for a write
operation. If the NM24C08U/09U is still busy with the write
operation no ACK will be returned. If the NM24C08U/09U has
completed the write operation an ACK will be returned and the
host can then proceed with the next read or write operation.
Write Protection (NM24C09U Only)
Programming of the upper half of the memory will not take place
if the WP pin of the NM24C09U is connected to VCC. The
NM24C09U will accept slave and byte addresses; but if the
memory accessed is write protected by the WP pin, the NM24C09U
will not generate an acknowledge after the first byte of data has
been received, and thus the program cycle will not be started when
the stop condition is asserted.
Byte Write (Figure 6)
Bus Activity:
Master
S
T
A
SLAVE
R ADDRESS
T
SDA Line
A
Bus Activity:
C
NM24C08U/09U
K
WORD
ADDRESS
A
C
K
S
T
DATA
O
P
A
C
K
DS800009-15
Page Write (Figure 7)
Bus Activity:
Master
SDA Line
S
T
A
SLAVE
R ADDRESS
T
Bus Activity:
NM24C08U/09U
WORD ADDRESS (n)
A
A
C
C
K
K
DATA n
DATA n + 1
S
T
DATA n + 15
O
P
A
A
A
C
C
C
K
K
K
DS800009-16
10
NM24C08U/09U Rev. B.1
www.fairchildsemi.com

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