24AA04/24LC04B
6.0
6.1
WRITE OPERATION
Byte Write
6.2
Page Write
Following the Start condition from the master, the
device code (4 bits), the block address (3 bits) and the
R/W bit, which is a logic-low, is placed onto the bus by
the master transmitter. This indicates to the addressed
slave receiver that a byte with a word address will
follow once it has generated an Acknowledge bit during
the ninth clock cycle. Therefore, the next byte transmit-
ted by the master is the word address and will be
written into the Address Pointer of the 24XX04. After
receiving another Acknowledge signal from the
24XX04, the master device will transmit the data word
to be written into the addressed memory location. The
24XX04 acknowledges again and the master
generates a Stop condition. This initiates the internal
write cycle and, during this time, the 24XX04 will not
generate Acknowledge signals (Figure 6-1).
The write control byte, word address and the first data
byte are transmitted to the 24XX04 in the same way as
in a byte write. But instead of generating a Stop condi-
tion the master transmits up to 16 data bytes to the
24XX04, which are temporarily stored in the on-chip
page buffer and will be written into memory once the
master has transmitted a Stop condition. Upon receipt
of each word, the four lower-order Address Pointer bits
are internally incremented by ‘
1
’. The higher-order 7
bits of the word address remain constant. If the master
should transmit more than 16 words prior to generating
the Stop condition, the address counter will roll over
and the previously received data will be overwritten. As
with the byte write operation, once the Stop condition is
received an internal write cycle will begin (Figure 6-2).
Note:
Page write operations are limited to writing
bytes within a single physical page
regardless
of the number of bytes
actually being written. Physical page
boundaries start at addresses that are
integer multiples of the page buffer size (or
‘page size’) and end at addresses that are
integer multiples of [page size – 1]. If a
page write command attempts to write
across a physical page boundary, the
result is that the data wraps around to the
beginning of the current page (overwriting
data previously stored there), instead of
being written to the next page as might be
expected. It is therefore necessary for the
application software to prevent page write
operations that would attempt to cross a
page boundary.
6.3
Write Protection
The WP pin allows the user to write-protect the entire
array (000-1FF) when the pin is tied to V
CC
. If tied to
V
SS
the write protection is disabled.
The Chip Scale package does not suport the write-
protect feature.
FIGURE 6-1:
Bus Activity
Master
S
T
A
R
T
BYTE WRITE
Control
Byte
Word
Address
S
T
O
P
P
A
C
K
A
C
K
A
C
K
Data
SDA Line
S
1
0
1
0
x
x
B0
0
Bus Activity
x
= “don’t care”
Block
Select
Bits
DS21708K-page 8
©
2009 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
