LM3S808 Datasheet, PDF (25/416 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S808 Microcontroller
1.4.1
1.4.1.1
1.4.1.2
1.4.1.3
1.4.2
1.4.2.1
ARM Cortex™-M3
Processor Core (see page 30)
All members of the Stellaris^® product family, including the LM3S808 microcontroller, are designed
around an ARM Cortex™-M3 processor core. The ARM Cortex-M3 processor provides the core for
a high-performance, low-cost platform that meets the needs of minimal memory implementation,
reduced pin count, and low-power consumption, while delivering outstanding computational
performance and exceptional system response to interrupts.
“ARM Cortex-M3 Processor Core” on page 30 provides an overview of the ARM core; the core is
detailed in the ARM® Cortex™-M3 Technical Reference Manual.
System Timer (SysTick)
Cortex-M3 includes an integrated system timer, SysTick. SysTick provides a simple, 24-bit
clear-on-write, decrementing, wrap-on-zero counter with a flexible control mechanism. The counter
can be used in several different ways, for example:
■ An RTOS tick timer which fires at a programmable rate (for example, 100 Hz) and invokes a
SysTick routine.
■ A high-speed alarm timer using the system clock.
■ A variable rate alarm or signal timer—the duration is range-dependent on the reference clock
used and the dynamic range of the counter.
■ A simple counter. Software can use this to measure time to completion and time used.
■ An internal clock source control based on missing/meeting durations. The COUNTFLAG bit-field
in the control and status register can be used to determine if an action completed within a set
duration, as part of a dynamic clock management control loop.
Nested Vectored Interrupt Controller (NVIC)
The LM3S808 controller includes the ARM Nested Vectored Interrupt Controller (NVIC) on the ARM
Cortex-M3 core. The NVIC and Cortex-M3 prioritize and handle all exceptions. All exceptions are
handled in Handler Mode. The processor state is automatically stored to the stack on an exception,
and automatically restored from the stack at the end of the Interrupt Service Routine (ISR). The
vector is fetched in parallel to the state saving, which enables efficient interrupt entry. The processor
supports tail-chaining, which enables back-to-back interrupts to be performed without the overhead
of state saving and restoration. Software can set eight priority levels on 7 exceptions (system
handlers) and 23 interrupts.
“Interrupts” on page 38 provides an overview of the NVIC controller and the interrupt map. Exceptions
and interrupts are detailed in the ARM® Cortex™-M3 Technical Reference Manual.
Motor Control Peripherals
To enhance motor control, the LM3S808 controller features Pulse Width Modulation (PWM) outputs.
PWM (see page 168)
Pulse width modulation (PWM) is a powerful technique for digitally encoding analog signal levels.
High-resolution counters are used to generate a square wave, and the duty cycle of the square
wave is modulated to encode an analog signal. Typical applications include switching power supplies
and motor control.
October 01, 2007
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Preliminary