Datasheet

 2007-2019 Microchip Technology Inc. DS20001708M-page 9
24AA04/24LC04B/24FC04
6.0 WRITE OPERATION
6.1 Byte Write
Following the Start condition from the master, the
device code (4 bits), the block address (2 bits, “don’t
care”, plus B0 bit) 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 after it has generated an
Acknowledge bit during the ninth clock cycle.
Therefore, the next byte transmitted 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).
6.2 Page Write
The write control byte, word address and first data byte
are transmitted to the 24XX04 in the same way as in a
byte write. However, instead of generating a Stop
condition, 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 the memory
once the master has transmitted a Stop condition.
Upon receipt of each word, the four lower-order
Address Pointer bits, which form the byte counter, are
internally incremented by one. The higher-order
four bits of the word address and bit B0 remain
constant. If the master should transmit more than 16
words prior to generating the Stop condition, the
Address Pointer 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).
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 support the hardware WP mode.
FIGURE 6-1: BYTE WRITE
Note: Page write operations are limited to writ-
ing 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.
S P
Bus Activity
Master
SDA Line
Bus Activity
S
T
A
R
T
S
T
O
P
Control
Byte
Word
Address
Data
A
C
K
A
C
K
A
C
K
1
0
1
0
xx
B0
0
x = “don’t care”
Block
Select
Bits