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6384E–ATARM–05-Feb-10
AT91SAM9G20
31.4.1
I/O Lines Description
31.5
Product Dependencies
31.5.1
I/O Lines
Both TWD and TWCK are bidirectional lines, connected to a positive supply voltage via a current
high. The output stages of devices connected to the bus must have an open-drain or open-col-
lector to perform the wired-AND function.
TWD and TWCK pins may be multiplexed with PIO lines. To enable the TWI, the programmer
must perform the following steps:
Program the PIO controller to:
– Dedicate TWD and TWCK as peripheral lines.
– Define TWD and TWCK as open-drain.
31.5.2
Power Management
Enable the peripheral clock.
The TWI interface may be clocked through the Power Management Controller (PMC), thus the
programmer must first configure the PMC to enable the TWI clock.
31.5.3
Interrupt
The TWI interface has an interrupt line connected to the Advanced Interrupt Controller (AIC). In
order to handle interrupts, the AIC must be programmed before configuring the TWI.
31.6
Functional Description
31.6.1
Transfer Format
The data put on the TWD line must be 8 bits long. Data is transferred MSB first; each byte must
be followed by an acknowledgement. The number of bytes per transfer is unlimited (see
FigureEach transfer begins with a START condition and terminates with a STOP condition (see
Figure A high-to-low transition on the TWD line while TWCK is high defines the START condition.
A low-to-high transition on the TWD line while TWCK is high defines a STOP condition.
Table 31-3.
I/O Lines Description
Pin Name
Pin Description
Type
TWD
Two-wire Serial Data
Input/Output
TWCK
Two-wire Serial Clock
Input/Output