MCP9804-ESLASHMS datasheet(13/54 Pages) MICROCHIP

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DS22203A-page 13

MCP9804

4.0

SERIAL COMMUNICATION

4.1

2-Wire Standard Mode I2C™

Protocol-Compatible Interface

The MCP9804 serial clock input (SCL) and the

bidirectional serial data line (SDA) form a 2-wire

bidirectional

Standard

mode

I2C

compatible

communication port (refer to the

Digital Input/Output

Pin Characteristics table and Sensor Serial

Interface Timing Specifications table).

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 tB-FREE.

This device does not support sequential register read/

write. Each register needs to be addressed using the

This device supports the Receive Protocol. The

read. Each repeated read or receive begins with a Start

condition and address byte. The MCP9804 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 MCP9804

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 MCP9804 releases the bus. All data

transfers are ended by a Stop condition from the

master.

4.1.4

ADDRESS BYTE

Following the Start condition, the host must transmit an

8-bit address byte to the MCP9804. The address for

the

MCP9804

Temperature

Sensor

‘0011,A2,A1,A0’ in binary, where the A2, A1 and A0

bits are set externally by connecting the corresponding

pins to VDD ‘1’ or GND ‘0’. The 7-bit address

transmitted in the serial bit stream must match the

selected address for the MCP9804 to respond with an

ACK. Bit 8 in the address byte is a read/write bit.

Setting this bit to ‘1’ commands a read operation, while

‘0’ commands a write operation (see Figure 4-1).

FIGURE 4-1:

Device Addressing.

TABLE 4-1:

MCP9804 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 MCP9804.

Transmitter Device sending data to the bus.

Receiver

Device receiving data from the bus.

START

A unique signal from 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 MCP9804

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.

678

SCL

SDA

1 A2A1A0

Start

Address Byte

Slave

Address

R/W

MCP9804 Response

Code

Address

See TABLE 3-2: “MCP9804 Address Byte”

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