Computer ports -(Serial)-

While most new computers sold in 2010, will not have serial -/- parallel ports, you might wonder why serial-ports might be of interest. Most industrial automation still use the RS-232 and RS-485 protocols for network communications, monitoring and control systems, (amongst others).

Not claiming to be an expert of these technologies, just a keen interest in placing industrial-hardware, .. juxtaposed with consumer-grade electronics.

pinouts serial port
+ pinouts serial port +

Found this nice simple explanation of ‘computer-ports’ – (Esp serial-ports) in, ..

SOURCE – Chapter 22 How Computers Work – (Millennium Edition)
Author – Ron White | Illustrated by Timothy Edward Downs
PUBLISHED: – First Printing: September 1999 –

Historically, the serial port is the jack-of-all-trades among computer components. It is simple in concept: one line to send data, another line to receive data, and a few other lines to regulate how data is sent over the other two lines. Because of its simplicity, the serial port has been used at one time or another to make a PC communicate with just about any device imaginable-from commonplace modems and printers to plotters and burglar alarms. And while it may be slow compared to a parrallel port, a serial port is fine for modems, that can only push signals across a telephone line serially, and for a mouse and digital camera, which dont need to send large quantities of data.

The serial port of often referred to an an RS-232 port. RS-232 is the Electronic Industries Association’s designation for a standard for how the various connectors in a serial port are to be used. But the fact that both 9-pin and 25-pin connectors are used as serial ports shows that we still have a long way to go before settling on exactly what constitues an RS-232 port. One of the drawbacks to both parallel and serial ports is that, for practical purposes, you’re limited to having two of each. The serial port functions are likely to migrate to the Univeral Serial Bus. The USB allows dozens of devices to be daisy chained from a single port.

+ pic-serial-port +


NOTE-1; – Click PLC (Programable Logic Controllers) – for related post in this category

NOTE-2; – the images (If clicked upon) – open in a new window (Or tabbed-page) where-upon those images were sourced.

A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.

Siemens provided industrial control package

Google-Search = Siemens provided industrial control package


Peter Melzer – Provides a nice over-view -/- insight into the Stuxnet-worm

Google-Search = large scale industrial processes

Today, U.S. national security planners are proposing that the 21st century’s critical infrastructure — power grids, communications, water utilities, financial networks — be similarly shielded from cyber marauders and other foes.

The ramparts would be virtual, their perimeters policed by the Pentagon and backed by digital weapons capable of circling the globe in milliseconds to knock out targets.


From source;

DCE (Data Communications Equipment) and DTE (Data Terminal Equipment) are descriptions of the role an Ethernet interface plays in 2-way communication.

DCE is typically the upstream device (network end), and DTE the downstream device (user end).  DTE is an end station, while DCE is a server, router, or hub.  But this can vary


Usually, the DTE device is the terminal (or a computer emulating a terminal), and the DCE is a modem.

DTE is usually a male connector and DCE is a female connector.

A general rule is that DCE devices provide the clock signal (internal clocking) and the DTE device synchronizes on the provided clock (external clocking). D-sub connectors follow another rule for pin assignment.

* 25 pin DTE devices transmit on pin 2 and receive on pin 3
* 25 pin DCE devices transmit on pin 3 and receive on pin 2
* 9 pin DTE devices transmit on pin 3 and receive on pin 2
* 9 pin DCE devices transmit on pin 2 and receive on pin 3

UPDATE; – Sat 17 April 2010 ->>> <<< This site has the BEST (And technically accurate) information that I have seen. It includes diagrams and the history of the standard as it has evolved, and is a great reference (If you need this sort of thing)

For my own reference;- (This link at the talks about – “a router to router connection” – which includeds the DTE vs DCE terminology – HERE >>> <<<

UPDATED: –  00:15am Thur 14 Oct 2010 –  Created a new-category” titled PLC tonight, .. and added this post DTE vs DCE as I consider this to be “A LIKE” topic of interest.