Hardware manual

Serial HOWTO
David S.Lawyer [e-mail] original by Greg Hankins
v2.27 February 2011
This document is for the UART serial port. This port has mostly disappeared from desktops and laptops is still
used elsewhere such as for embedded systems. It covers information other than that 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, etc. about the Serial Port•
1.5 Feedback•
1.6 What is a Serial Port?•
2. Quick Help
3. How the Hardware Transfers Bytes
3.1 Transmitting•
3.2 Receiving•
3.3 The Large Serial Buffers•
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•
4.10 The Serial Port is Now Obsolete on PCs•
4.11 RS-232 Cable Is Low Speed & Short Distance•
4.12 Inefficient PCI Interface to the Computer (in some cases)•
Serial HOWTO 1