Lucent Technologies MN10285K User Manual

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Figure 13-2 shows an example of an I

2

C bus configuration using two microcon-

trollers. Both I

2

C bus lines, SDA and SCL are bidirectional lines, connected to a 

positive supply voltage via a pullup resistor. The open-drain output pins of the 

microcontrollers perform the wired-AND function on the bus. The software 
controls when each microcontroller operates as a transmitter or receiver, or 

whether is in master or slave mode.

Table 13-2 describes the four possible operating modes for devices on the I

2

C 

bus.

Master transmitter

Device that generates the serial transfer clock (SCL) signal and 

transmits serial data to a slave device in sync with SCL

Master receiver

Device that generates the SCL signal and receives serial data from 

a slave device in sync with SCL

Slave transmitter

Device that transmits data in sync with the SCL signal from the mas-

ter

Slave receiver

Device that receives data in sync with the SCL signal from the master

Data line (SDA)

Clock line (SCL)

R

Pullup

resistors

V

DD

R

Clock output

Clock input

Data
output

Data input

Clock output

Clock input

Data
output

Data input

Device 1

Device 2