RS232 Serial Interface

RS232 is specified to drive 10 meters while the Universal Serial Bus [USB] only travels out to 4 meters, but you could use a hub to extend the USB cable. For longer distances without a hub I'd recommend using either the RS422 interface or RS485 interface. The down side to using either RS422 or RS485 with a computer is the requirement for an additional expansion card that provides these interfaces as neither come standard on a PC. 

RS232 Search Trends, Google

Still most computers are not shipping with a RS232 connector on the rear panel any longer. Dell computers dropped the RS232 interface in 2006, while Apple Computer dropped it in 2005. Users always have the option of adding an expansion card to their computer to add RS232 capability. The term RS232 which happens to be in common usages was changed to EIA232 in the 1970's. The 'RS' in RS232 means Recommended Standard, while EIA refers to Electronic Industries Alliance. EIA-232 is the correct usage to refer to the bus, and TIA/EIA-232 is the official term. The Acronym TIA refers to the Telecommunications Industry Association[1].

Internet Interest

Any how, the graphic above is Google search history [Trends^[2]] for the term RS232, note the decline in searches over the last five years. The phrase RS232 is about the only search term that can be used to indicate the interest in the RS-232 interface. Searching for EIA232 returns no results which means it lacks enough search volume, and the term '232' just returns to many unrelated results. Of course the number of people searching for a term does not really mean much, as most people do not even know what the connector on the back of the computer is ~ they just know it's missing when they have a cable that doesn't fit the other connectors. The original post follows below^[3]: Additional Interface Bus Trends [search history].

PC Back Panel Cut-Out

Chassis Cut-Out

 The picture shown to the left depicts the back panel I/O found on many newer mother boards. Comparing that picture with the one at the bottom of this article and the difference becomes obvious. The RS-232 and IEEE-1284 connectors have been replaced by a heat sink. The video interface has also been removed.

It makes perfect sense to remove the RS232 interface and the other two connectors from the back of computers. The video interface is normally found on the video card, so the 15-pin D-sub connector is not required. Many video cards ship with a Digital Video Interface [DVI] and a Video Graphic Adapter [VGA] connector, so why have another one the mother board. The 25-pin parallel port connector is out dated. Many new printers ship with an Ethernet port [or USB port] which is much faster then the

DIN PS2 Connectors

IEEE-1284 interface bus. With over 6 USB ports to handle any required peripheral, and 2 circular PS2 DINs to accommodate a keyboard and mouse the RS-232 interface is just not required. The PS2 interface replaced the RS232 interface as a mouse port in the 1980's. Low end PCs designed to keep costs low may still have a video interface designed into the motherboard providing a video port with out the need for a video card.

Chassis Back-Panel

When you add all this up, the benefit to removing these out-dated interfaces translate to higher speed peripheral connections, reduced cost by eliminating 3 large connectors, and the better use of the motherboard back panel.

In the three different mother boards I looked at the free space was taken up by a heat sink and fan. The space freed up by removing the three connectors now has an OTES [Outside Thermal Exhaust System] port which appears as a heat sink [external to the case], two small fans and a heat pipe running to the motherboard chipset residing inside the chassis, used to vent heat from the chip set Integrated Circuits [IC].


The Apple computers removed the RS232 bus and IEEE-1284 [Printer Port] bus some time ago. The RS232 interface is obsolete and should not be used for new designs. The IEEE-1284 interface is also obsolete. The 15-pin VGA interface is also out-dated on the newer mother boards. Each of these interfaces should start to disappear next year on main-stream personal computers... Of course there will always be a niche market.

Another View Point

The following text represents a comment left after the original posting of this article on a blog. Keep in mind that the current article has been expanded since then, and that the entire text from the commenter is not included here.

Anonymous comment said...

I disagree. While RS232 may be dying in the consumer world, it is found everywhere in industry, even in new designs. I bought a laptop three weeks ago, and one of the primary factors in deciding what to buy was having an onboard serial port so I wouldn't have to carry around an often unreliable USB to serial adapter. RS232, and especially RS485 and RS422, while possibly not even on the radar anymore in the consumer world, are

RS422 / RS485 Search Trends

guaranteed to be alive and kicking in commercial/industrial/military applications for years to come.....

The same applies for 1284, though admittedly to a lesser extent. I watched a company buy 17 new computers for employees who each had their own printer at their desks without checking if the computers came with 1284 ports. They ended up buying 17 USB to parallel adapters because it made more sense than throwing away all the older printers that still work great....

Let's never take anything out of Apple's playbook. If people want a Mac, they'll buy one, and they'll be so preoccupied with the things Apple tells them they can do on it that they can't think of the things Apple won't let them do.... End of comment.

Military Options

Military equipment is very different than commercial gear. The military may require a new computer, but still have it communicate with a 10 year old rack of gear. So older interfaces tend to stay around longer in military systems. Commercial customers may upgrade their systems once every four to five years, while a military system may be fielded for 10 to 15 years before it's upgraded or replaced. Military systems are up-graded in blocks, so each new block upgrade may only enhance a part of the system or the same system that was just upgraded. However, the entire system may be up-graded at the same time, but it really depends on the cost and how the contract was let.

Standards Information

The correct standards name when referring to the 232 interface is EIA-232, although widely used, the term RS232 is out-dated^[4]. Even more correct is TIA/EIA-232[letter], where the letter indicates the revision level ~ 'F' at this point in time. The RS series of standards was used up until the 70's, at which point they were switched over to the new EIA series.

EIA is an acronym for Electronic Industries Alliance^[5], one of a number of Standards organizations operating in the US^[6].

Other Buses in Decline

There are other PC buses in decline, or not appearing on many systems being shipped. The obsolete AGP video bus is a good example, replaced by the PCIe bus. Some percentage of consumers may want a new PC with an out-dated bus to port their expensive AGP card to the new system. But, if you incur the expense of a new computer why start with a slower video interface.

HDD Throughput Rates and Introduction Dates

Hard Drive

The IDE Hard Disk Drive [HDD] interface is yet another example of an interface you may not find on your PC. Although you would only know this one was missing if your tried to plug in your old hard drive. The IDE [or ATA] connector resides on the mother board, inside the PC case [as a 40-pin connector]. The IDE bus [ATA in the graph] was replaced by the faster Serial ATA interface [SATA] a few years ago [note the speed improvement].

Floppy Drive

The Floppy Disk Drive is also not being shipped on many new computers [Technical description of a Floppy interface]. A USB thumb drive may store up to 8GB of data compared to the physically much larger Floppy drive

USB Floppy Drive

which only stores 1.44MB of data. However there are still manufacturers of Floppy Drives, if the need is there. The common solution is to purchase an external Floppy Drive with a USB interface to the main PC. External drives may also be found to interface to the parallel port on the PC as well, just like the old

Zip Drive Search Trends from Google

Zip Drives[7]. It appears that Zip drives are still on the market [250MB or 750MB capacity] and now use the USB or ATAPI interface. ATAPI is the CD portion of the IDE interface and means AT Attachment with Packet Interface.

The military defines D subminiature connectors under the MIL-C-24308D specification [Manufacturers of Military Dsub Connectors ]. Basically MIL24308 specifies the identical connector that may be found on a personal computer [Dsub Mechanical Dimensions ]. However there are other options; for example, MIL-DTL-83513 specifies a micro-D connector that could replace the larger Dsub connector defined under MIL-24308 [MIL-DTL-83513 Dimensions ]. Newer equipment would benefit from using a smaller size connector with the same amount of pins. More recently the DOD released the MIL-DTL-32139 standard that specified a nano-D connector, with even smaller dimensions [MIL-DTL-32139 Dimensions ]. So the government provides an upgrade path while staying with the 'D' style of connector. Unfortunately commercial users really don't have the same option to upgrade, with millions of normal D-sub cables being sold. So USB was the only option for commercial PCs, even as D-sub have been getting smaller and faster [signal wise].

MIL-DTL-83513 Standard Connector

Why would a PC manufacturer upgrade to a more expensive connector just to save a little rear panel space. Plus the vendor would also have to supply a new expensive cable to connect to the new connector. Finally the interface [RS232 for example] does not really benefit from the higher quality connector, its best speed is already defined by the standard and is achievable by the low cost Dsub connector currently shipped with PCs.

The D-subminiature connector is a large connector, for the number of pins it handles. All the new computer interface buses are serial buses and use a different type of connector. Normal D-Sub interfaces run at a few hundred kilo-hertz [kHz] while newer buses run in the hundred of Mega-hertz [MHz] range; For example Serial-ATA [SATA ], FireWire [IEEE-1394 ], and even the Universal Serail Bus [USB ] run at much higher rates.

Interface IC

Yes there are one dollar RS232 interface ICs and yes you may have a five year old computer, but it's time for a change. Television went from black-and-white to color, and now from analog to digital. 

Why not design a circuit that will pass a decent data rate and is upgradable to another interface. Implementing a USB interface is definitely the way to go.

Google provides the Search Trends used above, however the author added the colored text to indicate the search term. The trend lines provide an interesting way of visualizing the amount of interest in a particular topic. The graphs are normalized so there is no way to see the amount of interest or traffic for a particular term, but it's very easy to see a trend. The trend in people searching for RS232 data has been decreasing sense 2004; however 2004 is the earliest date a term can be tracked.

Reference;  http://www.google.com/trends