9

PRELIMINARY

AT91SAM7A1 Summary

6048AS–ATARM–07/04

Controller Area

Network (CAN)

The AT91SAM7A1 provides one CAN (2.0A and 2.0B). These are serial communica-

tions protocols that efficiently support distributed real-time control with a very high level

of security (16 mailboxes). The main features are:

•

Prioritization of messages

•Multi-master

•

System wide data consistency

•

Error detection and error signaling

•

Automatic retransmission of corrupted messages

•

Automatic reply after receive a remote frame

•

Time stamp on each transfer

•

Multicast reception with time synchronization

•

Continuous reception mode

General-purpose

Timer (GPT)

The AT91SAM7A1 features three general-purpose timers. Each timer can be indepen-

dently programmed to perform a wide range of functions including frequency

measurement, event counting, interval measurement, pulse generation, delay timing

and pulse width modulation.

Each general-purpose timer has one external clock input, five internal clock inputs, and

three multi-purpose input/output signals that can be configured by the user. Each timer

drives an internal interrupt signal that can be programmed to generate processor inter-

rupts via the GIC (Generic Interrupt Controller).

Three general-purpose timers are grouped in the same block. This block has two global

registers that act upon all three GPTs. The Block Control Register allows the three tim-

ers to be started simultaneously with the same instruction. The Block Mode Register

defines the external clock inputs for each timer, allowing them to be chained.

Simple Timer (ST)

Simple Timers provide basic functions for timing calculation. Each channel of this timer

has a specific prescalar and a 16-bit counter. The prescalar defines the clock frequency

of the channel counter. The 16-bit counter starts down-counting when a value different

to zero is loaded. An interrupt is generated when the counter is null.

Capture Module

(CAPT)

The capture module is a frame analyzer. It stores the period of time between two edges

of a signal in a register. This period is described as a number of counter cycles. The

capture allows data transfers with the PDC.

Pulse Width

Modulator (PWM)

The AT91SAM7A1 includes four PWM channels. Each channel can generate pulses.

The frequency and the duty cycle of each channel can be configured.

Watch Timer (WT)

The watch timer provides a seconds counter and an alarm function. The alarm register

has a resolution of 30.5 µs. This allows a 32-bit register to have sufficient range to cater

for a 24 or 36 hour period.

Watchdog (WD)

The AT91SAM7A1 has an internal watchdog that can be used to prevent system lock-up

if the software becomes trapped in a deadlock.