Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems When the Universal Serial Bus (USB) took hold in the late 1990s, many predicted that serial ports would soon be obsolete. Plenty of peripherals that formerly used the serial port have switched to USB. But some devices can't use USB, or have requirements that USB alone can't provide. Many embedded systems use serial ports because they're inexpensive and less complex to program compared to USB. Serial ports can use longer cables than USB allows. And the RS-485 serial interface supports networks suitable for many monitoring and control applications. While most PCs no longer have built-in serial (COM) ports, the ports are easy to add via USB converters. With converters, the number of expansion slots no longer limits the number of serial ports a system can have. The SerialPort class included in Microsoft's .NET Framework shows that PC applications continue to find COM-port communications useful. What's Inside This book explores wide and varied territory, including hardware and software; ports in PCs and in embedded systems; and RS-232, RS-485, and wireless interfaces. You don't need to read the book straight through. If you're interested in a particular topic, you can skip right to it. The first chapters focus on hardware and interfacing. Chapters 1 and 2 are an introduction to asynchronous serial communications. Chapter 3 discusses serial ports in PCs, and chapters 4–8 are a guide to interfacing using RS-232, RS-485, and wireless technologies. The next chapters are a guide to programming. Chapters 9 and 10 show how to program serial ports on PCs using Visual Basic .NET and Visual C# .NET. Chapter 11 shows how to program serial ports for embedded systems with examples for microEngineering Labs' PICBASIC PRO compiler and Microchip Technology's MPLAB C18 C compiler. Chapters 12 and 13 focus on hardware and programming for RS-485 serial networks. Chapters 14–16 explain how to implement USB virtual COM ports using special-purpose and generic USB controllers. What's New in the Second Edition Much has happened in the world of computing since the first edition of this book was released. For this second edition, author Jan Axelson has revised and updated the contents from start to finish. One addition is example code in C/C# as well as Basic. This book includes code examples for PCs and for embedded systems (microcontrollers). Also new in the Second Edition are these topics: - Designing and programming USB virtual COM ports.
- Using wireless technologies to transmit serial data.
- Accessing serial ports over Ethernet or Wi-Fi networks.
- Transferring any kind of text data using Unicode encoding.
Who Should Read this Book? Whether your interest is hardware or software, and whether you work with PCs, embedded systems, or both, you'll find useful guidance in this book. - Programmers will learn how to communicate via serial ports, including USB virtual COM ports, in PCs and embedded systems. The example code for PCs and microcontrollers in Basic and C/C# provides a quick start for a variety of applications.
- Circuit designers will find designs for a variety of applications including converters that translate between RS-232, RS-485, and 3V/5V logic. Designs with fail-safe features, high noise immunity, and low power consumption are included.
- Hobbyists and experimenters will find inspiration for projects.
- Teachers and students can learn about serial ports and use the examples in this book to demonstrate concepts.
This book assumes you have a basic knowledge of electronics and either Basic/Visual Basic or C/C# programming. No previous knowledge or experience with serial-port hardware or programming is required. Table of Contents Introduction Acknowledgments 1. Options and Choices When to use a Serial Port System Components - The Computers
- The Physical Link
- Programming
Applications - Example Systems
- Managing Communications
- Special-purpose Modules
2. Formats and Protocols Sending Serial Data - Asynchronous and Synchronous Communications
- Word Formats
- Bit Rate and Baud Rate
- System Support for Low-level Protocols
Sending Bits - The Format
- The Need for Accurate Timing
- Autodetecting the Bit Rate
- Autodetecting a COM Port
Data Formats - Binary Data
- Text Data
- ASCII Hex
- Application-specific Protocols
Preventing Missed Data - Flow Control
- Buffers
- Event-driven Programming and Polling
- Acknowledgments
- Error Checking
3. COM Ports on PCs Port Architecture - Device Manager
- Port Resources
- Serial Servers
Accessing Ports - Drivers
- Identifying Ports
- GUIDs for COM Ports
- COM Port Numbering
- INF Files
- Options for Application Programming
4. Inside RS-232 The Hardware Interface - Signals
- Voltages
- Timing Limits
Converting Voltages - Interface Chips
- Short-range Circuits
Port-powered Circuits - Using Outputs as a Power Source
- Regulating the Voltage
Alternate Interfaces - Direct Connection
- Other Unbalanced Interfaces
5. Designing RS-232 Links Connectors and Adapters - Connector Options
- Adapters
- Using Microcontroller Development Boards
Cables - Length Limits
- Surge Protection
Isolated Lines - Ways to Achieve Isolation
- About Grounds
- Power Supply Grounds
- Optoisolating
Debugging Tools - Using a Breakout Box
- Monitoring with a Voltmeter
- Oscilloscopes and Logic Analyzers
6. Inside RS-485 About RS-485 - Balanced and Unbalanced Lines
- Voltage Requirements
- Current and Power
- Speed
- Internal Protection Circuits
Interfacing Options - Chips
- Adding a Port on a PC
- Converting 3.3/5V Logic
- Converting RS-232
Controlling the Driver Enable - Re-enabling the Driver
- Software-assisted Control
- Hardware Control
7. Designing RS-485 Links and Networks Long and Short Lines - When Is a Line Long?
- Calculating Line Length
- Choosing a Driver Chip
Line Terminations - Characteristic Impedance
- Adding a Termination
- Effects of Terminations
- Reflections
- Series Terminations
- Terminations for Short Lines
- AC Terminations
- Network Topologies
Biasing the Line - Open-circuit Protection
- Short-circuit Protection
Cable Types - How a Wire Picks Up Noise
- Twisted-pair Cable
- Selecting Cable
Grounds and Differential Lines - Ensuring a Common Ground
- Isolated Lines
Using Multiple Buses - Adding a Repeater
- Implementing a Star Topology
8. Going Wireless Media and Modulation - Using a Carrier Frequency
- Spread Spectrum Technology
- Ensuring Reliable Transfers
Infrared - Transmitters and Receivers
- IrDA
Radio Frequency - Complying with Regulations
- Choosing an RF Band
- Implementing a Link
- Using Other RF Standards
9. Using .NET's SerialPort Class Gaining Access to a Port - Finding Ports
- Opening a Port
- Timeouts
- Receive Threshold
- Closing a Port
Transferring Data - Transferring Bytes
- Transferring Text
Using Stream Objects - BinaryReader and BinaryWriter
- StreamReader and StreamWriter
Saving a Port and Parameters - The Application Settings Architecture
- Combo Box Example
10. Managing Ports and Transfers in .NET Receiving Data - Setting Timeouts
- Detecting Received Data
- Collecting Received Data
- Ensuring Efficient Transfers
Sending Data - Avoiding Timeouts
- Sending without Blocking the Application
- Preventing Buffer Overflows
- Ensuring Efficient Transfers
Flow Control - Selecting a Method
- Monitoring and Controlling the Signals
Handling Errors - Exceptions
- The ErrorReceived Event
- Verifying Received Data
Structuring an Application - Defining a ComPorts Class
- Setting Parameters with Combo Boxes
- Defining Application-specific Events
11. Ports for Embedded Systems A Microcontroller Serial Port - About the PIC18F4520
- The Enhanced UART
Registers - Configuring and Accessing the Port
- Setting the Bit Rate
- Interrupts
- Basic Operations
Accessing a Port - Configuring the Port
- Sending Data
- Receiving Data
- Using Interrupts
- Using Flow Control
Adding Ports - Multiple On-chip UARTs
- Firmware UARTs
- External UARTs
12. Network Programming Managing Traffic - Steps in Exchanging a Message
- Protocols
- Using Existing Protocols
- Debugging Tips
Addressing - Assigning Addresses
- Detecting Addresses
- Reserving Address Values
- Defining a Message Format
- 9-bit Format
13. An RS-485 Network Connecting the Nodes - Transceivers
- Terminating and Biasing
- Cabling
Example Protocol Commands - Reading a Byte
- Writing a Byte
Polling the Nodes - Configuring the Driver-enable Line
- Sending Commands
Responding to Polls - Auxiliary Routines
- Decoding Received Data
14. Inside USB Hosts and Devices - Assigning a Driver on the Host
- Requirements
- Host Responsibilities
- Device Responsibilities
- Speed
- Endpoints
USB Transfers - Transfer Types
- Transactions
- The Data Toggle
15. Using Special-function USB Controllers Inside the Chips - Serial Interface (FT232R)
- Parallel Interface (FT245R)
- Prototyping Modules
Using the Controllers - Drivers
- Adding Vendor-specific Data
- Implementing a Virtual COM Port
- Converting from RS-232 to USB
16. Using Generic USB Controllers The Communication Devices Class - Documentation
- Overview
- Device Controllers
- Host Drivers
Using the Abstract Control Model - POTS Models
- Virtual COM Ports
- Requests
- Notifications
- Maximizing Performance
Descriptors and INF Files - Device Descriptor
- Configuration Descriptor
- Communication Class Interface Descriptors
- Data Class Interface Descriptors
- String Descriptors
- The INF File
- Composite Devices
Index Paperback; 380 pages.
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