24AA08/24LC08B
5.0
DEVICE ADDRESSING
FIGURE 5-1:
A control byte is the first byte received following the
Start condition from the master device (Figure 5-1).
The control byte consists of a four-bit control code. For
the 24XX08, 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). B2 is a “don’t
care” for the 24XX08. They are used by the master
device to select which of the four 256 word-blocks of
memory are to be accessed. These bits are in effect the
three Most Significant bits of the word address.
The last bit of the control byte defines the operation to
be performed. When set to ‘
1
’ a read operation is
selected. When set to ‘
0
’ a write operation is selected.
Following the Start condition, the 24XX08 monitors the
SDA bus, checking the device type identifier being
transmitted and, upon receiving a ‘
1010’
code, the
slave device outputs an Acknowledge signal on the
SDA line. Depending on the state of the R/W bit, the
24XX08 will select a read or write operation.
Operation
Read
Write
Control
Code
Block Select
Block Address
Block Address
R/W
CONTROL BYTE
ALLOCATION
Read/Write Bit
Block
Select
Bits
x
B1 B0 R/W ACK
Control Code
S
1
0
1
0
Slave Address
Start Bit
x = “don’t care”
Acknowledge Bit
1010
1010
1
0
FIGURE 5-2:
ADDRESS SEQUENCE BIT ASSIGNMENTS
Control Byte
Address Low Byte
1
0
1
0
X
B1 B0
R/W
A
7
•
•
•
•
•
•
A
0
Control
Code
x = “don’t care”
Block
Select
bits
©
2009 Microchip Technology Inc.
DS21710J-page 7
MICROCHIP [ MICROCHIP TECHNOLOGY ]
