ATmega1284P datasheet(209/468 Pages) ATMEL

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209

8152G–AVR–11/09

ATmega164PA/324PA/644PA/1284P

20. 2-wire Serial Interface

20.1

Features

• Simple Yet Powerful and Flexible Communication Interface, only two Bus Lines Needed

• Both Master and Slave Operation Supported

• Device can Operate as Transmitter or Receiver

• 7-bit Address Space Allows up to 128 Different Slave Addresses

• Multi-master Arbitration Support

• Up to 400 kHz Data Transfer Speed

• Slew-rate Limited Output Drivers

• Noise Suppression Circuitry Rejects Spikes on Bus Lines

• Fully Programmable Slave Address with General Call Support

• Address Recognition Causes Wake-up When AVR is in Sleep Mode

20.2

2-wire Serial Interface Bus Definition

The 2-wire Serial Interface (TWI) is ideally suited for typical microcontroller applications. The

TWI protocol allows the systems designer to interconnect up to 128 different devices using only

two bi-directional bus lines, one for clock (SCL) and one for data (SDA). The only external hard-

ware needed to implement the bus is a single pull-up resistor for each of the TWI bus lines. All

devices connected to the bus have individual addresses, and mechanisms for resolving bus

contention are inherent in the TWI protocol.

Figure 20-1. TWI Bus Interconnection

20.2.1

TWI Terminology

The following definitions are frequently encountered in this section.

Device 1

Device 2

Device 3

Device n

SDA

SCL

........

Table 20-1.

TWI Terminology

Term

Description

Master

The device that initiates and terminates a transmission. The Master also generates the

SCL clock.

Slave

The device addressed by a Master.

Transmitter

The device placing data on the bus.

Receiver

The device reading data from the bus.

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