at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 417

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

31.4.1
Table 31-3.
31.5
31.5.1
31.5.2
31.5.3
31.6
31.6.1
6384B–ATARM–15-Dec-08
Pin Name
TWD
TWCK
Product Dependencies
Functional Description
I/O Lines Description
I/O Lines
Power Management
Interrupt
Transfer Format
I/O Lines Description
Both TWD and TWCK are bidirectional lines, connected to a positive supply voltage via a current
source or pull-up resistor (see
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:
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.
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.
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
31-4).
Each transfer begins with a START condition and terminates with a STOP condition (see
31-3).
• Program the PIO controller to:
• Enable the peripheral clock.
• 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.
– Dedicate TWD and TWCK as peripheral lines.
– Define TWD and TWCK as open-drain.
Pin Description
Two-wire Serial Data
Two-wire Serial Clock
Figure 31-2 on page
AT91SAM9G20 Preliminary
416). When the bus is free, both lines are
Input/Output
Input/Output
Type
Figure
Figure
417