24AA16 Datasheet, PDF (5/12 Pages) Microchip Technology – 16K 1.8V I 2 C O Serial EEPROM

24AA16
3.6 Device Addressing
A control byte is the first byte received following the start
condition from the master device. The control byte con-
sists of a 4-bit control code, for the 24AA16 this is set as
1010 binary for read and write operations. The next three
bits of the control byte are the block select bits (B2, B1,
B0). They are used by the master device to select which
of the eight 256 word blocks of memory are to be
accessed. These bits are in effect the three most signifi-
cant bits of the word address. It should be noted that the
protocol limits the size of the memory to eight blocks of
256 words, therefore the protocol can support only one
24AA16 per system.
The last bit of the control byte defines the operation to
be performed. When set to one a read operation is
selected, when set to zero a write operation is selected.
Following the start condition, the 24AA16 monitors the
SDA bus checking the device type identifier being
transmitted, upon a 1010 code the slave device outputs
an acknowledge signal on the SDA line. Depending on
the state of the R/W bit, the 24AA16 will select a read
or write operation.
Operation
Control
Code
Block Select
R/W
Read
Write
1010
Block Address
1
1010
Block Address
0
FIGURE 3-2: CONTROL BYTE
ALLOCATION
START
READ/WRITE
SLAVE ADDRESS
R/W A
1
0
1
0
B2 B1 B0
X = Don’t care
4.0 WRITE OPERATION
4.1 Byte 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
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 24AA16. After receiving
another acknowledge signal from the 24AA16 the mas-
ter device will transmit the data word to be written into
the addressed memory location. The 24AA16 acknowl-
edges again and the master generates a stop condi-
tion. This initiates the internal write cycle, and during
this time the 24AA16 will not generate acknowledge
signals (Figure 4-1).
4.2 Page Write
The write control byte, word address and the first data
byte are transmitted to the 24AA16 in the same way as
in a byte write. But instead of generating a stop condi-
tion the master transmits up to sixteen data bytes to the
24AA16 which are temporarily stored in the on-chip
page buffer and will be written into the memory after the
master has transmitted a stop condition. After the
receipt of each word, the four lower order address
pointer bits are internally incremented by one. The
higher order seven bits of the word address remains
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 inter-
nal write cycle will begin (Figure 4-2).
FIGURE 4-1:
BUS ACTIVITY
MASTER
BYTE WRITE
S
T
A
R
CONTROL
BYTE
T
WORD
ADDRESS
SDA LINE
S
A
BUS ACTIVITY
C
K
FIGURE 4-2:
BUS ACTIVITY
MASTER
SDA LINE
PAGE WRITE
S
T
A _CONTROL
R
BYTE
T
S
BUS ACTIVITY
WORD
ADDRESS (n)
A
A
C
C
K
K
DATA n
S
DATA
T
O
P
P
A
A
C
C
K
K
DATA n + 1
S
T
DATA n + 15
O
P
P
A
A
A
C
C
C
K
K
K
© 1996 Microchip Technology Inc.
DS21054E-page 5