MCP47FXB2XT-EST datasheet(109/124 Pages) MICROCHIP

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DS20006368A-page 109

MCP47FXBX4/8

APPENDIX B: I2C SERIAL

INTERFACE

This I2C interface is a two-wire interface that allows

multiple devices to be connected to this two-wire bus.

Figure B-1 shows a typical I2C interface connection.

FIGURE B-1:

TYPICAL I2C INTERFACE.

B.1

Overview

A device that sends data onto the bus is defined as

transmitter, and a device receiving data is defined as

receiver. The bus must be controlled by a master

device which generates the Serial Clock (SCL),

controls the bus access and generates the Start and

Stop conditions. Devices that do not generate a serial

clock work as slave devices. Both master and slave

can operate as transmitter or receiver, but the master

device

determines

which

mode

activated.

Communication is initiated by the master (micro-

controller), which sends the Start bit followed by the

slave address byte. The first byte transmitted is always

the slave address byte, which contains the device

code, the address bits and the R/W bit.

The I2C interface specifies different communication bit

rates. These are referred to as Standard, Fast or High-

Speed modes. The MCP47FXBX4/8 supports these

three modes. The clock rates (bit rate) of these modes

are:

• Standard mode: up to 100 kHz (kbit/s)

• Fast mode: up to 400 kHz (kbit/s)

• High-Speed mode (HS mode): up to 3.4 MHz

(Mbit/s)

The I2C protocol supports two addressing modes:

• 7-bit slave addressing

• 10-bit slave addressing (allows more devices on

the I2C bus)

Only 7-bit slave addressing will be discussed in this

section.

The I2C serial protocol allows multiple master devices

on the I2C bus. This is referred to as Multi-master. For

this, all master devices must support Multi-master

operation. In this configuration, all master devices mon-

itor their communication. If they detect that they wish to

transmit a bit that is a logic high but is detected as a

logic low (some other master device driving), they “get

off” the bus. That is, they stop their communication and

continue to listen to determine if the communication is

directed towards them.

The I2C serial protocol only defines the field types, field

lengths, timings, etc. of a frame. The frame content

defines the behavior of the device. For details on the

frame content (commands/data), refer to Section 7.0

“I2C Device Commands”.

The I2C serial protocol defines some commands called

“General Call Addressing”, which allows the master

device to communicate to all slave devices on the I2C

bus.

SCL

Slave

SDA

Master

Typical I2C Interface Connections

Other Devices

Note:

Refer

the

NXP

Specification

#UM10204, Rev. 03 19 June 2007

document for more details on the I2C

specifications.

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