ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 213

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

22.2.1
22.2.2
9223B–AVR–09/11
TWI Terminology
Electrical Interconnection
The following definitions are frequently encountered in this section.
Table 22-1.
The PRTWI bit in
enable the 2-wire Serial Interface.
As depicted in
pull-up resistors. The bus drivers of all TWI-compliant devices are open-drain or open-collec-
tor. This implements a wired-AND function which is essential to the operation of the interface.
A low level on a TWI bus line is generated when one or more TWI devices output a zero. A
high level is output when all TWI devices tri-state their outputs, allowing the pull-up resistors to
pull the line high. Note that all AVR devices connected to the TWI bus must be powered in
order to allow any bus operation.
The number of devices that can be connected to the bus is only limited by the bus capacitance
limit of 400 pF and the 7-bit slave address space. A detailed specification of the electrical char-
acteristics of the TWI is given in
different sets of specifications are presented there, one relevant for bus speeds below
100kHz, and one valid for bus speeds up to 400kHz.
Term
Master
Slave
Transmitter
Receiver
Atmel ATmega48PA/88PA/168PA [Preliminary]
TWI Terminology
Figure
Description
The device that initiates and terminates a transmission. The Master also generates the
SCL clock.
The device addressed by a Master.
The device placing data on the bus.
The device reading data from the bus.
“Minimizing Power Consumption” on page 42
22-1, both bus lines are connected to the positive supply voltage through
“Two-wire Serial Interface Characteristics” on page
must be written to zero to
321. Two
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