M24256-BR3MN6T datasheet(5/19 Pages) STMICROELECTRONICS

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M24256-B, M24128-B

Up to eight memory devices can be connected on

a single I2C bus. Each one is given a unique 3-bit

code on its Chip Enable inputs. When the Device

Select Code is received on the SDA bus, the mem-

ory only responds if the Chip Select Code is the

same as the pattern applied to its Chip Enable

pins.

The 8th bit is the RW bit. This is set to ‘1’ for read

and ‘0’ for write operations. If a match occurs on

the Device Select Code, the corresponding mem-

ory gives an acknowledgment on the SDA bus dur-

ing the 9th bit time. If the memory does not match

the Device Select Code, it deselects itself from the

bus, and goes into stand-by mode.

There are two modes both for read and write.

These are summarized in Table 6 and described

later. A communication between the master and

the slave is ended with a STOP condition.

Each data byte in the memory has a 16-bit (two

byte wide) address. The Most Significant Byte (Ta-

ble 4) is sent first, followed by the Least significant

Byte (Table 5). Bits b15 to b0 form the address of

the byte in memory. Bit b15 is treated as a Don’t

Care bit on the M24256-B memory. Bits b15 and

b14 are treated as Don’t Care bits on the M24128-

B memory.

Write Operations

Following a START condition the master sends a

Device Select Code with the RW bit set to ’0’, as

shown in Table 6. The memory acknowledges this,

and waits for two address bytes. The memory re-

sponds to each address byte with an acknowledge

bit, and then waits for the data byte.

Writing to the memory may be inhibited if the WC

input pin is taken high. Any write command with

WC=1 (during a period of time from the START

condition until the end of the two address bytes)

will not modify the memory contents, and the ac-

companying data bytes will

not be acknowledged,

as shown in Figure 5.

Byte Write

In the Byte Write mode, after the Device Select

Code and the address bytes, the master sends

one data byte. If the addressed location is write

protected by the WC pin, the memory replies with

a NoAck, and the location is not modified. If, in-

stead, the WC pin has been held at 0, as shown in

Figure 6, the memory replies with an Ack. The

master terminates the transfer by generating a

STOP condition.

Page Write

The Page Write mode allows up to 64 bytes to be

written in a single write cycle, provided that they

are all located in the same ’row’ in the memory:

Table 3. Device Select Code 1

Note: 1. The most significant bit, b7, is sent first.

Device Type Identifier

Chip Enable

Device Select Code

Table 4. Most Significant Byte

Note: 1. b15 is treated as Don’t Care on the M24256-B series.

b15 and b14 are Don’t Care on the M24128-B series.

Table 5. Least Significant Byte

b15

b14

b13

b12

b11

b10

Table 6. Operating Modes

Note: 1. X =

VIH or VIL.

Mode

RW bit

WC 1

Data 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

≤ 64

START, Device Select, RW = ‘0’

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