Datasheet

 2009-2019 Microchip Technology Inc. DS20001711L-page 8
24AA01/24LC01B/24FC01
5.0 DEVICE ADDRESSING
A control byte is the first byte received following the
Start condition from the master device. The control byte
consists of a four-bit control code. For the 24XX01, this
is set as ‘
1010’ binary for read and write operations.
The next three bits of the control byte are “don’t cares”
for the 24XX01. The combination of the 4-bit control
code and the next three bits are called the slave
address.
The last bit of the control byte is the Read/Write
(R/W)
bit and it 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 24XX01 monitors the SDA bus, checking
the device type identifier being transmitted. Upon
receiving a valid slave address and the R/W
bit, the
slave device outputs an Acknowledge signal on the
SDA line. Depending on the state of the R/W bit, the
24XX01 will select a read or write operation.
The next byte received defines the address of the first
data byte within the selected block (Figure 5-2).
Because only A6…A0 are used, the upper address bit
is a “don’t care”.
FIGURE 5-1: CONTROL BYTE
ALLOCATION
FIGURE 5-2: ADDRESS SEQUENCE BIT ASSIGNMENTS
Operation
Control
Code
Block Select R/W
Read 1010 Block Address 1
Write 1010 Block Address 0
10 10
xxx
R/W
ACK
Start Bit
Read/Write
Bit
x = “don’t care”
S
Slave Address
Acknowledge Bit
Control Code
Block
Select
Bits
1 010
x
x
R/W
A
6
A
0
•••• •
Control Byte
Word Address Byte
Control
Code
Block
Select
bits
x = “don’t care”
x
x