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?2011 Microchip Technology Inc.

DS25095A-page 13

MCP9808

4.0

SERIAL COMMUNICATION

4.1

2-Wire Standard Mode I

Protocol Compatible Interface

The MCP9808 Serial Clock (SCL) input and the

bidirectional Serial Data (SDA) line form a 2-wire

bidirectional, Standard mode, I

C compatible

communication port (refer to the Digital Input/Output

Pin Characteristics and Sensor Serial Interface

Timing Specifications tables).

The following bus protocol has been defined:

4.1.1

DATA TRANSFER

Data transfers are initiated by a Start condition

(START), followed by a 7-bit device address and a

read/write bit. An Acknowledge (ACK) from the slave

confirms the reception of each byte. Each access must

be terminated by a Stop condition (STOP).

Repeated communication is initiated after t

B-FREE

This device does not support sequential register

read/write. Each register needs to be addressed using

the Register Pointer.

This device supports the receive protocol. The register

can be specified using the pointer for the initial read.

Each repeated read or receive begins with a Start

condition and address byte. The MCP9808 retains the

previously selected register. Therefore, it outputs data

from the previously specified register (repeated pointer

specification is not necessary).

4.1.2

MASTER/SLAVE

The bus is controlled by a master device (typically a

microcontroller) that controls the bus access and

generates the Start and Stop conditions. The MCP9808

is a slave device and does not control other devices in

the bus. Both master and slave devices can operate as

either transmitter or receiver. However, the master

device determines which mode is activated.

4.1.3

START/STOP CONDITION

A high-to-low transition of the SDA line (while SCL is

high) is the Start condition. All data transfers must be

preceded by a Start condition from the master. A

low-to-high transition of the SDA line (while SCL is

high) signifies a Stop condition.

If a Start or Stop condition is introduced during data

transmission, the MCP9808 releases the bus. All data

transfers are ended by a Stop condition from the

master.

TABLE 4-1:

MCP9808 SERIAL BUS

PROTOCOL DESCRIPTIONS

Term

Description

Master

The device that controls the serial bus,

typically a microcontroller.

Slave

The device addressed by the master,

such as the MCP9808.

Transmitter Device sending data to the bus.

Receiver

Device receiving data from the bus.

START

A unique signal from the master to

initiate serial interface with a slave.

STOP

A unique signal from the master to

terminate serial interface from a slave.

Read/Write A read or write to the MCP9808

registers.

ACK

A receiver Acknowledges (ACK) the

reception of each byte by polling the bus.

NAK

A receiver Not-Acknowledges (NAK) or

releases the bus to show End-of-Data

(EOD).

Busy

Communication is not possible

because the bus is in use.

Not Busy

The bus is in the Idle state; both SDA

and SCL remain high.

Data Valid SDA must remain stable before SCL

becomes high in order for a data bit to

be considered valid. During normal

data transfers, SDA only changes state

while SCL is low.

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