Hardware manual

21. Other Serial Devices (not async RS-232)
21.1 Successors to RS-232•
21.2 EIA-422-A (balanced) and EIA-423-A (unbalanced)•
21.3 EIA-485•
21.4 EIA-530•
21.5 EIA-612/613•
21.6 The Universal Serial Bus (USB)•
21.7 Firewire•
21.8 MIDI•
21.9 Synchronization & Synchronous•
22. Other Sources of Information
22.1 Books•
22.2 Serial Software•
22.3 Related Linux Documents•
22.4 Serial Mailing List•
22.5 Internet•
23. Appendix A: Very Obsolete Hardware/Software
23.1 Replacing pre 1990 UARTS•
23.2 Two Ports with the Same IO address•
23.3 Configuring by modifying source code•
23.4 Modems on Multiport Cards Obsolete for Sending at 56k•
23.5 Lock-Files if you used the depreciated devfs•
23.6 Devfs (The deprecated Device File System. History)•
1. Introduction
This HOWTO covers basic info on the serial port which is missing on newer personal computers but is being
used in recent embedded systems as well as for routers, point-of-sale equipment, etc. It includes multiport
serial cards. It was written when the serial port was a major port for connecting a PC to modems and printers,
etc. and the style of this article reflects this. If you're having problems with the serial port, want to understand
how it works, or need a detailed introduction to it before studying serial programming, this is one place to find
out about it.
This HOWTO is about the original serial port which uses a UART chip and is sometimes called a "UART
serial port" to differentiate it from the newer types of serial devices: Universal Serial Bus or Firewire. It's slow
compared to newer serial devices but can send text several times faster than you can read it. Information
specific to devices which use serial ports: analog modems, text-terminals, infrared devices, and a few printers
are found in Modem-HOWTO, Text-Terminal-HOWTO, Infrared-HOWTO, and Printing-HOWTO. Info on
getty (the program that runs the login process or the like) has been also moved to other related HOWTOs
since mgetty and uugetty are best for modems while agetty is best for text-terminals. If you are dealing with a
modem, text terminal, infrared device, or printer, then you may not need to consult this HOWTO. But if you
are using the serial port for some other device, using a multiport serial card, trouble-shooting the serial port
itself, or want to understand more technical details of the serial port, then you may want to use this HOWTO
Serial HOWTO
21. Other Serial Devices (not async RS-232) 5