at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 252

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Product Dependencies
I/O Lines
Power
Management
Interrupt
Functional Description
Transfer Format
252
AT91RM3400
Table 41. I/O Lines Description
Both TWD and TWCK are bi-directional lines, connected to a positive supply voltage via a cur-
rent source or pull-up resistor (see Figure 80 on page 251). 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-
collector 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 eight bits long. Data is transferred MSB first; each byte
must be followed by an acknowledgement. The number of bytes per transfer is unlimited (see
Figure 82 on page 253).
Each transfer begins with a START condition and terminates with a STOP condition (see Fig-
ure 81 on page 252).
•
•
Figure 81. START and STOP Conditions
Pin Name
TWD
TWCK
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.
TWCK
TWD
Pin Description
Two-wire Serial Data
Two-wire Serial Clock
Start
Stop
Input/Output
Input/Output
1790A–ATARM–11/03
Type