5.1

Start condition

Start is identified by a falling edge of Serial Data (SDA) while Serial Clock (SCL) is stable in the high state. A Start

condition must precede any data transfer instruction. The device continuously monitors (except during a Write

cycle) Serial Data (SDA) and Serial Clock (SCL) for a Start condition.

5.2

Stop condition

Stop is identified by a rising edge of Serial Data (SDA) while Serial Clock (SCL) is stable and driven high. A Stop

condition terminates communication between the device and the bus master. A Read instruction that is followed

by NoAck can be followed by a Stop condition to force the device into the Standby mode.

A Stop condition at the end of a Write instruction triggers the internal Write cycle.

5.3

Data input

During data input, the device samples Serial Data (SDA) on the rising edge of Serial Clock (SCL). For correct

device operation, Serial Data (SDA) must be stable during the rising edge of Serial Clock (SCL), and the Serial

Data (SDA) signal must change only when Serial Clock (SCL) is driven low.

5.4

Acknowledge bit (ACK)

The acknowledge bit is used to indicate a successful byte transfer. The bus transmitter, whether it be bus master

receiver pulls Serial Data (SDA) low to acknowledge the receipt of the eight data bits.

5.5

Device 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 4 on serial data (SDA),

most significant bit first.

Device type identifier (1)

Chip enable address (2)

RW

b7

b6

b5

b4

b3

b2

b1

b0

1

0

1

0

C2

C1

C0

RW

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

2. b3, b2 and b1 are compared with the C2, C1 and C0 values programmed in the chip enable register.

When the device select code is received, the device responds only if the b3, b2 and b1 values match the values

of the C2, C1 and C0 bits programmed in the chip enable register.

time.

If the device does not acknowledge the device select code, the device de-selects itself from the bus, and goes

into standby mode (therefore will not acknowledge the device select code).

M24128X-FCU

Start condition

DS12680 - Rev 2

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