24AA128 Просмотр технического описания (PDF) - Microchip Technology

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24AA128

128K I2C™ CMOS Serial EEPROM

Microchip Technology 

24AA128/24LC128/24FC128

5.0 DEVICE ADDRESSING

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

24XX128, this is set as ‘1010’ binary for read and write

operations. The next three bits of the control byte are

the Chip Select bits (A2, A1, A0). The Chip Select bits

allow the use of up to eight 24XX128 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 corresponding A2,

A1 and A0 pins for the device to respond. These bits

are, in effect, the three Most Significant bits of the word

address.

For the MSOP package, the A0 and A1 pins are not

connected. During device addressing, the A0 and A1

Chip Select bits (Figures 5-1 and 5-2) should be set to

‘0’. Only two 24XX128 MSOP packages can be

connected to the same bus.

The last bit of the control byte defines the operation to

be performed. When set to a one, a read operation is

selected. 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). Because

only A13…A0 are used, the upper two address bits are

“don’t care” bits. The upper address bits are transferred

first, followed by the Less Significant bits.

Following the Start condition, the 24XX128 monitors

the SDA bus checking the device type identifier being

transmitted. Upon receiving a ‘1010’ code and

appropriate device select bits, the slave device outputs

an Acknowledge signal on the SDA line. Depending on

the state of the R/W bit, the 24XX128 will select a read

or write operation.

FIGURE 5-1:

CONTROL BYTE

FORMAT

Read/Write Bit

Control Code

Chip Select

Bits

S 1 0 1 0 A2 A1 A0 R/W ACK

Start Bit

Slave Address

Acknowledge Bit

5.1 Contiguous Addressing Across

Multiple Devices

The Chip Select bits A2, A1 and A0 can be used to

expand the contiguous address space for up to 1 Mbit

by adding up to eight 24XX128 devices on the same

bus. In this case, software can use A0 of the control

byte as address bit A14; A1 as address bit A15; and A2

as address bit A16. It is not possible to sequentially

read across device boundaries.

For the MSOP package, up to two 24XX128 devices

can be added for up to 256 Kbit of address space. In

this case, software can use A2 of the control byte as

address bit A16. Bits A0 (A14) and A1 (A15) of the

control byte must always be set to logic ‘0’ for the

MSOP.

FIGURE 5-2:

ADDRESS SEQUENCE BIT ASSIGNMENTS

Control Byte

Address High Byte

Address Low Byte

1

0

1

0

A

2

A

1

A

0

R/W

Control

Code

Chip

Select

Bits

x

x

A AA A

13 12 11 10

A

9

A

8

A

7

•

•

•

•

•

•

A

0

x = “don’t care” bit

 2010 Microchip Technology Inc.

DS21191S-page 7

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