Embedded System Development Lecture 4 1/31/2007 CS590 Embedded System Development Lecture 4 1/31/2007

Class Notes Course Project Mid-Term Document and Presentation are due Feb. 28. Homework Number 1 is out and due Feb. 7. 2/3-Term Exam will be March 28th.

Universal Asynchronous Receiver/Transmitter A Universal Asynchronous Receiver/Transmitter or UART is a common device on many systems. Its purpose is to convert data to and from a serial interface, that is, an interface on which the bits that make up the data are sent one after another. Let’s look at the data sheet.

A System with a UART

RS-232 Standard for serial binary data interconnection between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). Standard requires the transmitter to use +12V and -12V, but requires the receiver to distinguish voltages as low as +3V and -3V.

RS-232 Logic one is defined as a negative voltage. This signal condition is called marking. It has the functional significance of OFF. Logic zero is defined as a positive voltage. This signal condition is called spacing. It has the functional significance of ON.

RS-232 Signals TxD – Transmit Data RxD – Receive Data RTS – Request To Send CTS – Clear To Send DTR – Data Terminal Ready DSR – Data Set Ready CD – Carrier Detect RI – Ring Indicator

RS-232 Some Issues The large voltage swings and requirement for positive and negative voltages increase power consumption and complicate power supply design. Single-ended signaling referenced to a common signal ground limit noise immunity and transmission distance.

RS-232 Some Issues Multi-drop (meaning a connection between more than two devices) operation of an RS-232 compatible interface is not defined; while multi-drop “work - arounds” have been devised, they have limitations in speed and compatibility.

RS-485 RS-485 is a physical layer electrical specification. The standard specifies a differential form of signaling. The difference between the wires voltages is what conveys the data. It supports multi-drop communications. It offers high data transmission speeds (35 Mbits/s up to 10 m and 100kbits/s at 1200 m)

RS-485 Since it uses a differential balanced line over twisted pair, it can span relatively large distances (up to 4000 feet). RS-485 drives need to be put in transmit mode explicitly by asserting a signal to the driver. Can be made full-duplex by using four wires.

Real-time Clock Provides a system with “clock time”. Needs power when the system is off. Sometimes will have a small amount of non-volatile memory.

Switches and Bouncing Switches provide an inexpensive input method. Switches “bounce”.

Multiplexed Switches Switches can be wired individually or wired in a matrix. There are tradeoffs with each method.

Optical Encoders Allow you to detect movement. Can give both speed and direction information.

Light Emitting Diode A Light-Emitting Diode (LED) is a semiconductor device that emits light when electrically biased in the forward direction. LEDs are made from a variety of semiconductor materials that produce different colors of light.

Light Emitting Diode LEDs have an extremely long life span: upwards of 100,000 hours. Used for general illumination as well as for data display. May not be appropriate for low power devices.

Light Emitting Diode Available in many different form factors. Easy to control. Generate their own light.

Liquid Crystal Display A Liquid Crystal Display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices.

Liquid Crystal Display LCD modules have different controller interfaces. LCDs need external light. Capable of controlling the contrast of the display. Some LCDs have a slow response speed. Some LCDs have a limited viewing angle.

RC Servos Provide a precisely controllable mechanical output. Controlled by three wires: Power (red) Ground (black) Control (white)

RC Servos Pulses sent over the control wire set the position of the servo arm. The servo expects a pulse about every 20 ms. The length of the pulse determines the position of the servo arm. 1.5 ms – neutral position >1.5 ms – moves in one direction <1.5 ms moves in other direction

Stepper Motors A Stepper Motor is a motor that can divide a full rotation into a large number of steps. Two types: Unipolar – Four separate electromagnets, current is sent in only one direction. Bipolar – Two separate electromagnets, current will flow in one direction then the other.

Stepper Motors Given the same size, a bipolar motor will be more powerful. One part of a dynamic mechanical system. Controllers are available that essentially reduce control down to direction and step signals.

Class Project Any questions from last week? Demo Boards may be signed out by each team. Microchip Forums

Project Team 1 Osama Abouelkheir Anne-Marie Buibish John Mallinger Anthony Megna

Project Team 2 Steve Gardner Andrew Marcum Seth Schapiro Erik Certain

Project Team 3 John Bodenschatz Elhadi Elomda Mary Green Richard Hoffman

Project Team 4 Angelyn Begley Michael Carsten Keith Shie