Rainbow Electronics AT91CAP9S250A - Manual (Page 485)

485
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
34.4 Application Block Diagram
Figure 34-2. Application Block Diagram
34.4.1 I/O Lines Description
34.5 Product Dependencies
34.5.1 I/O Lines
Both TWD and TWCK are bidirectional lines, connected to a positive supply voltage via a current
source or pull-up resistor (see
Figure 34-2 on page 485 ). When the bus is free, both lines are
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.
34.5.2 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.
34.5.3 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.
Table 34-3. I/O Lines Description
Pin Name Pin Description Type
TWD Two-wire Serial Data Input/Output
TWCK Two-wire Serial Clock Input/Output
Host with
TWI
Interface
TWD
TWCK
Atmel TWI
Serial EEPROM
I 2 C RTC
I 2 C LCD
Controller
Slave 1 Slave 2 Slave 3
Rp Rp
VDD
Rp: Pull up value as given by the I 2 C Standard
I 2 C Temp.
Sensor
Slave 4