24AA16/24LC16B
5.0
DEVICE ADDRESSING
Operation
Read
Write
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 24XX16, 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 Significant bits
(MSb) 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 24XX16 per system.
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 24XX16 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
24XX16 will select a read or write operation.
Control
Code
Block Select
Block Address
Block Address
R/W
1010
1010
1
0
FIGURE 5-1:
CONTROL BYTE
ALLOCATION
Read/Write Bit
Block
Select
Bits
B2 B1 B0 R/W ACK
Control Code
S
1
0
1
0
Slave Address
Start Bit
Acknowledge Bit
FIGURE 5-2:
ADDRESS SEQUENCE BIT ASSIGNMENTS
Control Byte
Address Low Byte
1
0
1
0
B
2
B
1
B
0 R/W
A
7
•
•
•
•
•
•
A
0
Control
Code
Block
Select
bits
©
2009 Microchip Technology Inc.
DS21703H-page 7
MICROCHIP [ MICROCHIP TECHNOLOGY ]
