24lc1025t-i-sm Microchip Technology Inc., 24lc1025t-i-sm Datasheet - Page 7

• Manufacturer Part Number: 24lc1025t-i-sm
• Description: 1024k I2c Cmos Serial Eeprom
• Manufacturer: Microchip Technology Inc.

5.0
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 4-bit control code; for the
24XX1025, this is set as ‘1010’ binary for read and
write operations. The next bit of the control byte is the
block select bit (B0). This bit acts as the A16 address
bit for accessing the entire array. The next two bits of
the control byte are the Chip Select bits (A1, A0). The
Chip Select bits allow the use of up to four 24XX1025
devices on the same bus and are used to select which
device is accessed. The Chip Select bits in the control
byte must correspond to the logic levels on the corre-
sponding A1 and A0 pins for the device to respond.
These bits are in effect the two Most Significant bits of
the word address.
The last bit of the control byte defines the operation to
be performed. When set to a one, a read operation is
selected, and when set to a zero, a write operation is
selected. The next two bytes received define the
address of the first data byte (Figure 5-2). The upper
address bits are transferred first, followed by the Less
Significant bits.
Following the Start condition, the 24XX1025 monitors
the SDA bus checking the device type identifier being
transmitted. Upon receiving a ‘1010’ code and appro-
priate device select bits, the slave device outputs an
Acknowledge signal on the SDA line. Depending on the
state of the R/W bit, the 24XX1025 will select a read or
write operation.
This device has an internal addressing boundary
limitation that is divided into two segments of 512K bits.
Block select bit ‘B0’ to control access to each segment.
FIGURE 5-2:
© 2007 Microchip Technology Inc.
1
Control
Code
DEVICE ADDRESSING
0
1
Control Byte
0
Select
Block
Bit
B
0
ADDRESS SEQUENCE BIT ASSIGNMENTS
A
1
Select
Chip
Bits
A
0 R/W
24AA1025/24LC1025/24FC1025
15
A
14
A
Address High Byte
13
A
Preliminary
12
A
11
A
10
A
FIGURE 5-1:
5.1
The Chip Select bits A1, A0 can be used to expand the
contiguous address space for up to 4 Mbit by adding up
to four 24XX1025’s on the same bus. In this case,
software can use A0 of the control byte as address bit
A16 and A1 as address bit A17. It is not possible to
sequentially read across device boundaries.
Each device has internal addressing boundary
limitations. This divides each part into two segments of
512K bits. The block select bit ‘B0’ controls access to
each “half”.
Sequential read operations are limited to 512K blocks.
To read through four devices on the same bus, eight
random Read commands must be given.
Start Bit
A
9
S
A
8
Contiguous Addressing Across
Multiple Devices
1
Control Code
0
A
7
Slave Address
1
•
CONTROL BYTE
FORMAT
Address Low Byte
•
0
Select
Block
•
Bits
B0
Read/Write Bit
X = “don’t care” bit
Acknowledge Bit
•
A1
Select
Chip
Bits
•
DS21941E-page 7
A0
•
R/W
A
0
ACK