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Serial HOWTO
David S.Lawyer
dave@lafn.org
original by Greg Hankins
v2.23 November 2004
This document describes the UART serial port features other than those which should be covered by Modem-HOWTO, PPP-HOWTO, Serial-Programming-HOWTO, or Text-Terminal-HOWTO. It lists info on multiport serial cards. It contains technical info about the serial port itself in more detail than found in the above HOWTOs and should be best for troubleshooting when the problem is the serial port itself. If you are dealing with a Modem, PPP (used for Internet access on a phone line), or a Text-Terminal, those HOWTOs should be consulted first.
1. Introduction
- 1.1 Copyright, Disclaimer, & Credits
- 1.2 New Versions of this Serial-HOWTO
- 1.3 New in Recent Versions
- 1.4 Related HOWTO's re the Serial Port
- 1.5 Feedback
- 1.6 What is a Serial Port?
2. Quick Help
3. How the Hardware Transfers Bytes
4. Serial Port Basics
- 4.1 What is a Serial Port ?
- 4.2 IO Address & IRQ
- 4.3 Names: ttyS0, ttyS1, etc.
- 4.4 Interrupts
- 4.5 Data Flow (Speeds)
- 4.6 Flow Control
- 4.7 Data Flow Path; Buffers
- 4.8 Complex Flow Control Example
- 4.9 Serial Driver Module
5. Is the Serial Port Obsolete?
- 5.1 Introduction
- 5.2 EIA-232 (RS-232) Cable Is Low Speed & Short Distance
- 5.3 Inefficient Interface to the Computer (in some cases)
6. Multiport Serial Boards/Cards/Adapters
- 6.1 Intro to Multiport Serial
- 6.2 Modem Limitations
- 6.3 Dumb vs. Smart Cards
- 6.4 Getting/Enabling a Driver
- 6.5 Multiport Devices in the /dev Directory,
- 6.6 Making Legacy Multiport Devices in the /dev Directory
- 6.7 Standard PC Serial Cards
- 6.8 Dumb Multiport Serial Boards (with standard UART chips)
- 6.9 Intelligent Multiport Serial Boards
- 6.10 Unsupported Multiport Boards
7. Servers for Serial Ports
8. Configuring Overview
9. Locating the Serial Port: IO address, IRQs
- 9.1 What Bus is my Serial Port On?
- 9.2 IO & IRQ Overview
- 9.3 PCI Bus Support
- 9.4 Common mistakes made re low-level configuring
- 9.5 IRQ & IO Address Must be Correct
- 9.6 What is the IO Address and IRQ per the driver ?
- 9.7 What is the IO Address & IRQ of my Serial Port Hardware?
- 9.8 Choosing Serial IRQs
- 9.9 Choosing Addresses --Video card conflict with ttyS3
- 9.10 Set IO Address & IRQ in the hardware (mostly for PnP)
- 9.11 Giving the IRQ and IO Address to Setserial
10. Configuring the Serial Driver (high-level) "stty"
11. Serial Port Devices /dev/tts/2 = /dev/ttyS2, etc.
- 11.1 Serial Port Names: ttyS4, tts/2, etc.
- 11.2 The PCI Bus
- 11.3 Devfs (The Device File System)
- 11.4 Legacy Serial Port Device Names & Numbers
- 11.5 More on Serial Port Names
- 11.6 USB (Universal Serial Bus) Serial Ports
- 11.7 Link ttySN to /dev/modem
- 11.8 Which Connector on the Back of my PC is ttyS1, etc?
- 11.9 Creating Devices In the /dev directory
12. Interesting Programs You Should Know About
- 12.1 Serial Monitoring/Diagnostics Programs
- 12.2 Changing Interrupt Priority
- 12.3 What is Setserial ?
- 12.4 Stty
- 12.5 What is isapnp ?
- 12.6 What is slattach?
13. Speed (Flow Rate)
14. Locking Out Others
- 14.1 Introduction
- 14.2 Lock-Files
- 14.3 Lock-Files if you use devfs
- 14.4 Change Owners, Groups, and/or Permissions of Device Files
15. Communications Programs And Utilities
16. Serial Tips And Miscellany
- 16.1 Serial Module
- 16.2 Serial Console (console on the serial port)
- 16.3 Line Drivers
- 16.4 Stopping the Data Flow when Printing, etc.
- 16.5 Known IO Address Conflicts
- 16.6 Known Defective Hardware
17. Troubleshooting
- 17.1 Serial Electrical Test Equipment
- 17.2 Serial Monitoring/Diagnostics
- 17.3 (The following subsections are in both the Serial and Modem HOWTOs)
- 17.4 My Serial Port is Physically There but Can't be Found
- 17.5 Extremely Slow: Text appears on the screen slowly after long delays
- 17.6 Somewhat Slow: I expected it to be a few times faster
- 17.7 The Startup Screen Show Wrong IRQs for the Serial Ports.
- 17.8 "Cannot open /dev/ttyS?: Permission denied"
- 17.9 "Operation not supported by device" for ttyS?
- 17.10 "Cannot create lockfile. Sorry"
- 17.11 "Device /dev/ttyS? is locked."
- 17.12 "/dev/tty? Device or resource busy"
- 17.13 "Input/output error" from setserial, stty, pppd, etc.
- 17.14 "LSR safety check engaged"
- 17.15 Overrun errors on serial port
- 17.16 Port gets characters only sporadically
- 17.17 Troubleshooting Tools
- 17.18 Almost all characters are wrong; Many missing or many extras
18. Interrupt Problem Details
- 18.1 Types of interrupt problems
- 18.2 Symptoms of Mis-set or Conflicting Interrupts
- 18.3 Mis-set Interrupts
- 18.4 Interrupt Conflicts
- 18.5 Resolving Interrupt Problems
19. What Are UARTs? How Do They Affect Performance?
- 19.1 Introduction to UARTS
- 19.2 Two Types of UARTs
- 19.3 FIFOs
- 19.4 Why FIFO Buffers are Small
- 19.5 UART Model Numbers
20. Pinout and Signals
- 20.1 Pinout of 9-pin and 25-pin serial connectors
- 20.2 Signals May Have No Fixed Meaning
- 20.3 Cabling Between Serial Ports
- 20.4 RTS/CTS and DTR/DSR Flow Control
- 20.5 Preventing a Port From Opening
21. Voltage Waveshapes
- 21.1 Voltage for a Bit
- 21.2 Voltage Sequence for a Byte
- 21.3 Parity Explained
- 21.4 Forming a Byte (Framing)
- 21.5 How "Asynchronous" is Synchronized
22. Other Serial Devices (not async EIA-232)
- 22.1 Successors to EIA-232
- 22.2 EIA-422-A (balanced) and EIA-423-A (unbalanced)
- 22.3 EIA-485
- 22.4 EIA-530
- 22.5 EIA-612/613
- 22.6 The Universal Serial Bus (USB)
- 22.7 Firewire
- 22.8 MIDI
- 22.9 Synchronization & Synchronous
23. Other Sources of Information
- 23.1 Books
- 23.2 Serial Software
- 23.3 Related Linux Documents
- 23.4 Usenet newsgroups:
- 23.5 Serial Mailing List
- 23.6 Internet
24. Appendix: Obsolete Hardware (prior to 1990) Info
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