Datasheet

152
ATmega8A [DATASHEET]
8159E–AVR–02/2013
21. Two-wire Serial Interface
21.1 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 400kHz 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
21.2 Overview
The TWI module is comprised of several submodules, as shown in Figure 21-1. All registers drawn in a thick line
are accessible through the AVR data bus.
Figure 21-1. Overview of the TWI Module
21.2.1 SCL and SDA Pins
These pins interface the AVR TWI with the rest of the MCU system. The output drivers contain a slew-rate limiter in
order to conform to the TWI specification. The input stages contain a spike suppression unit removing spikes
shorter than 50 ns. Note that the internal pull-ups in the AVR pads can be enabled by setting the PORT bits corre-
TWI Unit
Address Register
(TWAR)
Address Match Unit
Address Comparator
Control Unit
Control Register
(TWCR)
Status Register
(TWSR)
State Machine and
Status control
SCL
Slew-rate
Control
Spike
Filter
SDA
Slew-rate
Control
Spike
Filter
Bit Rate Generator
Bit Rate Register
(TWBR)
Prescaler
Bus Interface Unit
START / STOP
Control
Arbitration detection Ack
Spike Suppression
Address/Data Shift
Register (TWDR)