Serial HOWTO Serial HOWTO Table of Contents Serial HOWTO...................................................................................................................................................1 David S.Lawyer [email protected] original by Greg Hankins.....................................................................1 1. Introduction..........................................................................................................................................1 2. Quick Help...........................................................................................................................................1 3. How the Hardware Transfers Bytes.....................................................................................................1 4. Serial Port Basics.................................................................................................................................1 5. Multiport Serial Boards/Cards/Adapters..............................................................................................2 6. Servers for Serial Ports........................................................................................................................2 7. Configuring Overview.........................................................................................................................2 8. Locating the Serial Port: IO address, IRQs..........................................................................................2 9. Configuring the Serial Driver (high-level) "stty"................................................................................2 10. Serial Port Devices /dev/ttyS2, etc.....................................................................................................2 11. Interesting Programs You Should Know About................................................................................3 12. Speed (Flow Rate)..............................................................................................................................3 13. Locking Out Others............................................................................................................................3 14. Serial Communications Programs And Utilities................................................................................3 15. Serial Tips And Miscellany...............................................................................................................3 16. Troubleshooting.................................................................................................................................3 17. Interrupt Problem Details...................................................................................................................4 18. What Are UARTs? How Do They Affect Performance?..................................................................4 19. Pinout and Signals.............................................................................................................................4 20. Voltage Waveshapes..........................................................................................................................4 21. Other Serial Devices (not async RS-232)..........................................................................................5 22. Other Sources of Information............................................................................................................5 23. Appendix A: Very Obsolete Hardware/Software..............................................................................5 1. Introduction..........................................................................................................................................5 1.1 Copyright, Disclaimer, & Credits......................................................................................................6 Copyright...........................................................................................................................................6 Disclaimer.........................................................................................................................................6 Trademarks........................................................................................................................................6 Credits...............................................................................................................................................6 1.2 New Versions of this Serial-HOWTO...............................................................................................6 1.3 New in Recent Versions.....................................................................................................................7 1.4 Related HOWTO's, etc. about the Serial Port...................................................................................7 1.5 Feedback............................................................................................................................................7 1.6 What is a Serial Port?.........................................................................................................................7 2. Quick Help...........................................................................................................................................8 3. How the Hardware Transfers Bytes....................................................................................................8 3.1 Transmitting.......................................................................................................................................9 3.2 Receiving.........................................................................................................................................10 3.3 The Large Serial Buffers..................................................................................................................10 4. Serial Port Basics..............................................................................................................................11 4.1 What is a Serial Port ?......................................................................................................................11 Intro to Serial...................................................................................................................................11 Pins and Wires.................................................................................................................................11 RS-232 (EIA-232, etc.)...................................................................................................................12 4.2 IO Address & IRQ...........................................................................................................................12 4.3 Names: ttyS0, ttyS1, etc...................................................................................................................12 i Serial HOWTO Table of Contents Serial HOWTO 4.4 Interrupts.........................................................................................................................................12 4.5 Data Flow (Speeds)..........................................................................................................................13 4.6 Flow Control...................................................................................................................................14 Example of Flow Control................................................................................................................14 Symptoms of No Flow Control.......................................................................................................15 Hardware vs. Software Flow Control..............................................................................................15 4.7 Data Flow Path; Buffers...................................................................................................................15 4.8 Complex Flow Control Example.....................................................................................................16 4.9 Serial Driver Module.......................................................................................................................18 4.10 The Serial Port is Now Obsolete on PCs.......................................................................................18 4.11 RS-232 Cable Is Low Speed & Short Distance............................................................................18 4.12 Inefficient PCI Interface to the Computer (in some cases)............................................................19 5. Multiport Serial Boards/Cards/Adapters............................................................................................19 5.1 Intro to Multiport Serial...................................................................................................................19 5.2 Dumb vs. Smart Cards.....................................................................................................................19 5.3 Getting/Enabling a Driver................................................................................................................20 Introduction.....................................................................................................................................20 Build (compile) support into the kernel?.........................................................................................20 Using module support....................................................................................................................20