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Computer and device serial port hacking and resources

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This page started as a collection of notes I have compiled over my twenty plus years of working with RS-232 and serial ports of all kinds from VAXes down to Intel based desktops.

The RS-232-C (now known as EIA-232-E) specification has been around since 1977 and is based on level +/-5vdc signals. EIA-232-E is an asynchronous clock specification meaning that signals are sent irrespective of the clock of the remote device and consequently can drop signals by over or under-running the remote device. EIA-232's big brothers EIA-422-B (balanced) and EIA-423-B (unbalanced) are synchronous and require clock signals on pin 25.

Notes on RS-232 (later EIA RS-232-C and still later EIA/TIA-232-F), RS-422 serial connections and it's descendant Universal Serial Bus (USB).

See also my notes for using serial ports under Linux


For those that support serial ports or modems connected to serial ports I highly recommend the following:

  1. Obtain a good understanding of the signals and how they "handshake" for flow control.
  2. Purchase a "break out box", signal tester and possibly a BERT (bit-error rate tester). Note that with proliferance of digital and fiber circuits needing a BERT tester is almost obsolete any longer.
  3. A line analyzer might by quite useful if you have to diagnose character losses or learn to configure a foreign device.
  4. And finally the cookbook: "RS232 Made Easy" by Martin D. Seyer has been the defacto standard for many years.


"RS232 Made Easy" by Martin D. Seyer

Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems by Jan Axelson

USB Complete: Everything You Need to Develop Custom USB Peripherals by Jan Axelson

Linux Network Administrator's Guide, 2nd Edition (free online)



Source Code examples

Serial port sniffers: (KDE on Linux)

USB sniffers:

Discussion groups:

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Page last modified on September 02, 2018, at 12:44 PM EST