Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 11, NO. 6 / JUNE 1985 / PAGE 24

What's so standard about RS-232? (teletalk) Corey Sandler.

What's So Standard About RS-232?

Have you ever wondered why most medical doctors practice and practice until their handwriting (in Latin, no less!) is all undecipherable by mere patients like us? It is all part of the process of "mystification' by which the ordinary is made to seem extraordinary, and by which we suspend all ordinary measures of what 12 minutes of someone's time and a tongue depressor are really worth.

I've decided that it is professional mystification that is also at work in the computer communications filed--my final conclusion after nearly ten years of trying to figure out why something that is called the RS-232C "standard' is actually about as standardized as the Republican Party and the Supreme Soviet.

(Why, sure we sell standard RS-232C cables,' the computer store dealer told me. "Which one do you want? The RTS/DCE standard? The DTE standard? The IBM male to male DB-25? The IBM female to 9-pin C-shell? The gold standard?')

In my business as a writer on microcomputer topics, I am constantly installing and trying out new pieces of hardware and software in one or another computer. If I were to connect together all of the cables in my collection of "standard' RS-232C cords, they might reach from Silicon Valley to Boca Raton--but they probably wouldn't work together.

I have recently embarked on another great search for the proper cable to connect the RS-232C output (an unusual, round female DIN plug) on my laptop portable computer to the DB-25 input on a lightweight thermal printer. So far, no luck, but then again I've only been at it for three weeks.

Anyway, I decided to go to the record books. Here's what I found: the RS-232C specification is an Electronics Industries Association (EIA) Standard, put into effect back in the dinosaur age of computing, 1969. It was written to establish, once and for always, the official way to make an interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) using serial digital data transmission. In most cases today, a piece of DTE is more commonly referred to as a computer; an item of DCE is a modem or a printer.

The "standard' defined the EIA position on electrical signal characteristics, the mechanical elements of the connection, and a functional assignment for interchange circuits. Table 1 lists the official pin assignments as implemented in the official 25-pin DB-25 connector.

Now, that all sounds so very neat. All of the important elements of telecommunications are there--the transmit and receive channels, communication rate and signal quality checks, and the important back-and-forth "hand-shaking' connections. (This is how most computers communicate. Computer A: "Are you ready to receive?' Computer B: "Yes.' Computer A: "Look out, here it comes.' Computer B: "Got it. Want me to read it back to you?' And so on.)

Therefore, you might think, any computer or modem manufacturer who claimed to adhere to the RS-232C standard would be telling you and me that we could find that good old RTS signal over there on pin 4, and the ever-popular DTR across the way on pin 20. But, no . . .

Taking a page from Alice in Wonderland, the EIA says that there are actually 13 standard but different implementations of the signal connections for an RS-232C interface. They have designated them with letters from A to M. But just to make absolutely certain that even that attempt at standardization is of no value, they added an Interface Type Z. What is Z? Why, it's "anything else.'

We mere users get to pay outrageous prices (one local store gets 65 bucks for a three-foot "standard' cable), because it is all but impossible to have the right connection the first time.

Well, as a public service to the readers of this august publication, I'd like to let you all in on two trade secrets that just might save your job, your family life, or your computer.

The first is a wonderful little device called a Smart Cable, available from IQ Technologies Inc., 11811 N.E. First St., Suite 308, Bellevue, WA 98005. This little black box is definitely a creation from the witch doctor's back room. It sits between your basic DCE and DTE (computer and modem or printer, remember?) and somehow manages to figure out what is being sent on which wire from one device, and at the same time what is being expected on which wire on the other device. I don't understand it, but I'm quite willing to be mystified here, since it works in 95% of the cases I've tried.

And now I've been introduced to one more bit of American ingenuity: a set of fat white looseleaf binders called Micro Match from a company called Command Computer Corp., P.O. Box 5096, Philadelphia, PA, 19111. (215) 745-5555.

Want to know how to hook up a Novation J-Cat modem to the asynchronous communications card on the IBM PC? Why, look it up in the index and you'll find that it requires a "standard' RS-232C cable with pins 2, 3, 5, 6, 7, and 8 connected straight through. You'll also find specific mode, parity, switch, and jumper settings for the computer and for the modem, as well as general advice on serial cable grounding principles, length limits, and wire types.

Want to hook up an Altos Computer to that very same Novation J-Cat modem? Why, you need the "standard' RS-232C cable with pins 1 and 7 connected straight through, pins 2 and 3 crossed in each direction, and pin 20 on the computer side connected to pin 8 on the modem side.

I wish it weren't so, but until manufacturers can get their acts straight, the Micro Match blueprints and indexes should be required products as all computer dealerships. And, if your office or personal setup has a regular influx of new "standard' RS-232C devices, these books should pay for themselves in aggravation relief within minutes of receipt.

Pony Express Revisited

A stupendous battle between a couple of not-small contenders in the growing field of electronic mail utilities is in the making. Leading the pack is MCI Mail, an offshoot of the MCI long distance telephone service. Sniping from a bit back is EasyLink, from Western Union, which can draw its lineage directly back to the Pony Express. And soon to lumber onto the scene is the diversifying and hungry AT&T giant.

Speaking of the Pony Express, though, I find myself amused at the two latest services being offered by these electronic postal services.

EasyLink sent me an "Express Document,' a laser-printed hand-delivered envelope it says can wing its way from a personal computer to someone's personal hands in two hours or less.

They system works like this: I type a document into the memory of my computer (mine is made by IBM), dial up

The system works like this: I type a going through the discount long distance utility that connects our house out in the country to New York (MCI, as a matter of fact), and link to Western Union. The folks there bounce my message off a satellite or through a cable to an office somewhere near me where it is printed out and stuffed into an envelope. And then a delivery truck from DHL Worldwide Courier Express picks up the package and heads for the hills.

Well, it works--as does a similar four-hour service from MCI Mail--but it sounds like the Pony Express to me.

And then MCI fires back with a new service that they say is the latest thing in electronic communication: MCI Mail Alert.

Alert works like this: from my computer to the long distance utility to the MCI system and there into the electronic mailbox of the person I am sending the message to. And then a friendly operator at MCI will telephone the lucky recipient (up to three calls within a two-hour period) and tell him, "You have a message in your mailbox. Why don't you sign on and read it some time?'

It sure sounds like the way telegrams are delivered these days--isn't that Western Union's business?

Table: 1.