LM3S3748 Datasheet, PDF (36/753 Pages) List of Unclassifed Manufacturers – Microcontroller

Architectural Overview
1.4.2
1.4.2.1
1.4.2.2
Cortex-M3 processor, allowing for more effecient use of the processor and the expanded available
bus bandwidth. The μDMA controller can perform transfers between memory and peripherals. It
has dedicated channels for each supported peripheral and can be programmed to automatically
perform transfers between peripherals and memory as the peripheral is ready to transfer more data.
The μDMA controller also supports sophisticated transfer modes such as ping-pong and
scatter-gather, which allows the processor to set up a list of transfer tasks for the controller.
Motor Control Peripherals
To enhance motor control, the LM3S3748 controller features Pulse Width Modulation (PWM) outputs
and the Quadrature Encoder Interface (QEI).
PWM
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.
On the LM3S3748, PWM motion control functionality can be achieved through:
■ Dedicated, flexible motion control hardware using the PWM pins
■ The motion control features of the general-purpose timers using the CCP pins
PWM Pins (see page 603)
The LM3S3748 PWM module consists of four PWM generator blocks and a control block. Each
PWM generator block contains one timer (16-bit down or up/down counter), two comparators, a
PWM signal generator, a dead-band generator, and an interrupt/ADC-trigger selector. The control
block determines the polarity of the PWM signals, and which signals are passed through to the pins.
Each PWM generator block produces two PWM signals that can either be independent signals or
a single pair of complementary signals with dead-band delays inserted. The output of the PWM
generation blocks are managed by the output control block before being passed to the device pins.
CCP Pins (see page 303)
The General-Purpose Timer Module's CCP (Capture Compare PWM) pins are software programmable
to support a simple PWM mode with a software-programmable output inversion of the PWM signal.
Fault Pins (see “Fault Conditions”)
The LM3S3748 PWM module includes four fault-condition handling inputs to quickly provide
low-latency shutdown and prevent damage to the motor being controlled.
QEI (see page 657)
A quadrature encoder, also known as a 2-channel incremental encoder, converts linear displacement
into a pulse signal. By monitoring both the number of pulses and the relative phase of the two signals,
you can track the position, direction of rotation, and speed. In addition, a third channel, or index
signal, can be used to reset the position counter.
The Stellaris quadrature encoder with index (QEI) module interprets the code produced by a
quadrature encoder wheel to integrate position over time and determine direction of rotation. In
addition, it can capture a running estimate of the velocity of the encoder wheel.
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April 08, 2008
Preliminary