Two-wire Serial
Interface
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
Two-wire Serial Interface The Two-wire Serial Interface (TWI) is ideally suited for typical microcontroller applica-
tions. The TWI protocol allows the systems designer to interconnect up to 128 different
Bus Definition
devices using only two bi-directional bus lines, one for clock (SCL) and one for data
(SDA). The only external hardware 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 68. TWI Bus Interconnection
VCC
Device 1
Device 3
R1
R2
Device 2
Device n
........
SDA
SCL
TWI Terminology
The following definitions are frequently encountered in this section.
Table 64. 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.
160
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
