M24C08-125 datasheet(12/30 Pages) STMICROELECTRONICS

12 / 30 page

Device operation

M24C16-125 M24C08-125 M24C04-125 M24C02-125

12/30

Doc ID 022564 Rev 1

3.5

Memory addressing

To start communication between the bus master and the slave device, the bus master must

initiate a Start condition. Following this, the bus master sends the device select code, shown

in Table 2 (on Serial Data (SDA), most significant bit first).

The device select code consists of a 4-bit Device Type Identifier, and a 3-bit Chip Enable

“Address” (E2, E1, E0). To address the memory array, the 4-bit Device Type Identifier is

1010b.

Each device is given a unique 3-bit code on the Chip Enable (E0, E1, E2) inputs. When the

device select code is received, the device only responds if the Chip Enable Address is the

same as the value on the Chip Enable (E0, E1, E2) inputs. However, those devices with

larger memory capacities (the M24C16, M24C08 and M24C04) need more address bits. E0

is not available for use on devices that need to use address line A8; E1 is not available for

devices that need to use address line A9, and E2 is not available for devices that need to

use address line A10 (see Figure 2 and Table 2 for details). Using the E0, E1 and E2 inputs,

up to eight M24C02, four M24C04, two M24C08 or one M24C16 devices can be connected

to one I²C bus.

The 8th bit is the Read/Write bit (RW). This bit is set to 1 for Read and 0 for Write operations.

If a match occurs on the device select code, the corresponding device gives an

acknowledgment on Serial Data (SDA) during the 9th bit time. If the device does not match

the device select code, it deselects itself from the bus, and goes into Standby mode.

Table 3.

Operating modes

Mode

RW bit

WC(1)

X = VIH or VIL.

Bytes

Initial sequence

Current Address Read

Start, Device Select, RW = 1

Random Address Read

Start, Device Select, RW = 0, Address

reStart, Device Select, RW = 1

Sequential Read

≥ 1

Similar to Current or Random Address

Read

Byte Write

VIL

Start, Device Select, RW = 0

Page Write

VIL

≤16

Start, Device Select, RW = 0

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