ATmega8(L)
Overview of the
TWI Module
The TWI module is comprised of several submodules, as shown in Figure 76. All registers drawn
in a thick line are accessible through the AVR data bus.
Figure 76. Overview of the TWI Module
SCL
SDA
Spike
Filter
Spike
Filter
Slew-rate
Control
Slew-rate
Control
Bus Interface Unit
Bit Rate Generator
START / STOP
Spike Suppression
Prescaler
Control
Address/Data Shift
Register (TWDR)
Bit Rate Register
(TWBR)
Arbitration detection
Ack
Address Match Unit
Control Unit
Address Register
(TWAR)
Status Register
(TWSR)
Control Register
(TWCR)
State Machine and
Status control
Address Comparator
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 corresponding to the SCL and SDA pins, as
explained in the I/O Port section. The internal pull-ups can in some systems eliminate the need
for external ones.
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2486T–AVR–05/08
ATMEL [ ATMEL ]
