COMPUTE II ISSUE 2 / JUNE/JULY 1980

The Single-Board 6502

Eric Rehnke

Getting Hooked Up

Presumably, you already have a computer and a terminal (or a computer with a built-in CRT) and are looking for a modem. The minimum modem necessary will be an originate only, acoustically coupled style capable of handling the BELL 103 standard modem protocol (300 baud). This will permit access to the centralized information system and the hobbyist bulletin board service but will not allow communication with other hobbyists that have orginate-only modems.

You see, for modem systems to communicate with each other, certain conventions must be adhered to. The most important of these states that the system that originates the phone call has to be in the “orgininate” mode while the system answering the call should be in the “answer” mode. This originate/answer mode business has to do with the set of frequencies that's used to send the data and need not concern us here except to realize that to be able to receive calls as well as place them, you need both modes (orginate and answer) in your modem system.

Now modems can couple up to the telephone line in two ways: acoustically and directly.

With an acoustically coupled modem, you must usually place the telephone call manually and put the telephone handset into rubber cups on the modem when the telephone call is connected.

This type of modem is easiest to install, adequate for most applications, and available from several sources in the $150–$200 price range.

If you expect your computer/modem system to be able to automatically answer the phone to carry on a conversation with another system or even be able to automatically place phone calls to other systems without user intervention, you'll want a direct-coupled modem instead of an acoustically-coupled type.

Most direct-coupled modems plug into a modular style phone jack like your extension phone does and allow for full computer control of the line.

Keep in mind that to be completely legal, the modem MUST use a data coupler that has been registered with the FCC guys. Now that's important.

Having a fully automatic telephone system hooked to the old computer benefits you in several ways. First, you can take messages from other systems all day long while you're at work or out playing golf (of course, this presumes you have enough friends to make it all worthwhile). And secondly, your computer can place calls to your friendly local (or long distance) data base very late at night to take advantage of low activity and/or cheaper phone rates. You could even download the complete UPI news service to your disk so you can enjoy the up-to-the-minute news with your coffee in the morning. Since the data stream is happening at 300 baud, your computer could sit and scan for key words – picking out only what you're interested in reading about. Quite a bit more efficient than the newspaper. Wouldn't you say?

Anyhow, there are three modem manufacturers which seem interested in supporting the hobby/personal computer market. They are

U. S. Robotics Inc.
1035 W. Lake St.
Chicago, IL 60607
(312) 733-0497

NOVATION Inc.
18664 Oxnard St.
Tarzana, CA 91356
(213) 996-5060

TNW Corp.
5924 Quiet Slope Dr.
San Diego, CA 92129
(714) 225-1040

(TNW modem useable only with PET or other IEEE Bus computer)

There are other companies making modems for this market, such as D.C. Hayes but most of these are useable only with certain bus configurations such as Apple or S-100. If you have one of these machines, this part of this column won't prove very useful to you.

I placed a call to U.S. Robotics to get more data on their 300 baud, direct coupled modem and was treated very well. They expressed a willingness to help me with my application and even sent me all their technical literature on the promise that I'd sent them a $5.00 check. No, I didn't tell them that I wrote a column for COMPUTE II. As far as they knew, I was just another hobbyist.

I also had some contact with TNW Corporation. They manufacture stuff for the PET (or other IEEE Bus equipped computers) so their direct-couple modem didn't turn out to be as useful for my particular application. But, if you're looking to turn your PET into an electronic mail system, TNW has the software and hardware to do just that. I believe they are working very closely with the PCNet people so they should have some good software coming out.

As it turns out, the PCNet software protocol is a bit on the complicated side for those of us not well versed in the esoterics of network theory and the like, so having a software package alredy prepared looks mightly appealing.

My personal application for a modem includes use on the PCNet as well as checking into one of the large time sharing systems like the Source or MicroNet (or both). Since I may want to automatically access a data base late at night, the modem/telephone interface needs to be fully automated.

I'll be checking out modems for a while and will report my findings.