24AA256 Datasheet, PDF (7/12 Pages) Microchip Technology – 256K I 2 C CMOS Serial EEPROM

24AA256/24LC256
6.0 WRITE OPERATIONS
6.1 Byte Write
Following the start condition from the master, the
control code (four bits), the chip select (three bits), and
the R/W bit (which is a logic low) are clocked onto the
bus by the master transmitter. This indicates to the
addressed slave receiver that the address high byte will
follow after it has generated an acknowledge bit during
the ninth clock cycle. Therefore the next byte
transmitted by the master is the high-order byte of the
word address and will be written into the address
pointer of the 24xx256. The next byte is the least signif-
icant address byte. After receiving another acknowl-
edge signal from the 24xx256, the master device will
transmit the data word to be written into the addressed
memory location. The 24xx256 acknowledges again
and the master generates a stop condition. This ini-
tiates the internal write cycle, and, during this time, the
24xx256 will not generate acknowledge signals
(Figure 6-1). If an attempt is made to write to the array
with the WP pin held high, the device will acknowledge
the command but no write cycle will occur, no data will
be written, and the device will immediately accept a
new command. After a byte write command, the inter-
nal address counter will point to the address location
following the one that was just written.
6.2 Page Write
The write control byte, word address, and the first data
byte are transmitted to the 24xx256 in the same way as
in a byte write. But instead of generating a stop condi-
tion, the master transmits up to 63 additional bytes,
which are temporarily stored in the on-chip page buffer
and will be written into memory after the master has
transmitted a stop condition. After receipt of each word,
the six lower address pointer bits are internally incre-
mented by one. If the master should transmit more than
64 bytes 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 inter-
nal write cycle will begin (Figure 6-2). If an attempt is
made to write to the array with the WP pin held high, the
device will acknowledge the command but no write
cycle will occur, no data will be written, and the device
will immediately accept a new command subject to
TBUF.
6.3 Write Protection
The WP pin allows the user to write-protect the entire
array (0000-7FFF) when the pin is tied to VCC. If tied to
VSS or left floating, the write protection is disabled. The
WP pin is sampled at the STOP bit for every write com-
mand (Figure 1-1) Toggling the WP pin after the STOP
bit will have no effect on the execution of the write cycle.
FIGURE 6-1: BYTE WRITE
BUS ACTIVITY
MASTER
SDA LINE
S
T
A ^CONTROL
R
BYTE
T
S
1
0
1
0
A
2
AA
10
0
ADDRESS
HIGH BYTE
X
ADDRESS
LOW BYTE
S
T
DATA
O
P
P
BUS ACTIVITY
A
A
A
A
C
C
C
C
K
K
K
K
X = don’t care bit
FIGURE 6-2: PAGE WRITE
BUS ACTIVITY
MASTER
SDA LINE
S
T
A ^CONTROL
R
BYTE
T
S
1
0
1
0
A
2
A
1
A
0
0
ADDRESS
HIGH BYTE
X
BUS ACTIVITY
A
A
C
C
K
K
X = don’t care bit
ADDRESS
LOW BYTE
DATA BYTE 0
A
A
C
C
K
K
S
T
DATA BYTE 63 _O
P
P
A
C
K
© 1998 Microchip Technology Inc.
DS21203C-page 7