It used to be enough just to have a modem and figure out what com port it was on. But as the operator of a big BBS I get a lot of questions about init (initialization) strings and there proper use. I thought I would give an init and "AT" primer on the subject, so here is my "Init Cookbook".
First the good news, about 7 of the commands have fairly universal meaning. However as new features have been added to various modems the manufactures have set up their own variations on some things. So in addition to these remarks it is a good idea to check your manual as well.
The most universal of the "AT" or attention commands first specified by the modem manufacture Hayes for their revolutionary 300 baud Smartmodem was the command AT itself. Any time you type on the entry field of a communications program the command AT the modem should respond with an OK. If it doesn't, that probably means you have an addressing, cable or power problem.
Basically the AT command is used as a signal to the modem that what follows is a command, in some cases the AT is the only way you can communicate with the modem at all. This is particularly true for the newer internal modems. Prior to about 4 years ago, it was common to set the modem up with "DIP" (dual in-line package) switches, and this technique is still used by many external modems, however even the external modems will respond to the AT commands.
When you group several of the AT commands together you create something called a "string" of commands. Since these commands in a row or string are used at the beginning of a session they have become known as an initialization string. But because computer types strive for efficiency and compactness (and because we are sometimes both lazy and trying to cloud meaning) the term was shortened to init string and finally to "INIT"
Generally your communications package will throw this init string at the modem when you first start it up. That is why you often have to tell your communications package the exact name and model of your modem, so it can select the right codes to send.
So here goes. The init cookbook. Other than AT most sessions begin with ATDT (dial by tone) or ATD (dial) or ATPD (pulse dial). Using one of these codes will get your modem to dial the number you put after the ATDT. So if I wanted to dial my BBS One Crossroads Place I would enter ATDT (1-913) 663-1100 and the modem using the DTMF (dual tone modulated frequency) tones would call the BBS.
So why would you want to use the other variations. Well if you live in an area that doesn't support touch tone dialing, or you are having trouble getting through, try using the older pulse dialing method. And if you were calling with an ISDN (Integrated Services Digital Network) TA (terminal adaptor, like a modem but digital) you would not use DT for dial tone just D for dial. Our ISDN number would be reached by sending ATD (1-913) 664-5082.
The next most important command is probably ATH (hangup) if you can't hang up you have a problem. Most communications packages have standardized around ALT H to invoke this command. Now if your modem is not using a communications package and you are just sending commands out the serial port, to get to the point that you can send the ATH you will have to send +++ (3 plus's in a rapid sequence) to activate the communications mode escape sequence.
By the way sending three symbols fast is a common way to abort a session, you can try sending +++, --- or === to stop a connect or a doorway session. While these are not specifically commands for the modem, they are used by many systems to signal an abort. Sometimes stopping something is much harder than starting it!
When sending most of the following commands you will only use the "AT" in front of the first, as long as they all come in a valid string, (in a row without spaces) they will all be treated as commands. Here are the seven fairly universal commands:
Now we get into manufacturer specific stuff:
If you see &K3 or \Q3 or &R0 in your manual this is telling the system to enable the RTS/CTS hardware handshaking protocol (a set of rules). Hardware handshaking will normally give you a much faster session, and unfortunately Windows defaults to software handshaking, so you may want to change this.
If you see &Q5 or \N3 or \N9, then the modem will use V.42 or MNP-5 data compression and error coding. Some people call this the auto-reliable mode as the modem will fall back (negotiate) the best connection it can.
And if you see &B1 or \J0 this will lock the baud rate. This is a little complicated, but the speed the computer talks to the modem at is often greater than the actual rate of the modem. For instance, if the modem is a 14,400 BPS unit, you often lock the baud rate at 19,200 to 57,600 depending on the amount of compression the modem and session will deliver. Often a 14,400 modem will using compression achieve data transfer rates up to 57,600 and a 28,800 modem can reach 115,200 although few BBS's actually scan this fast. We scan our ports at 57,600 BPS. Send a "WZ" to see the DCE (data communications speed rather than the DTR (data terminal ready speed).
I hope all of this actually sheds a little light on what the init string is all about. See if you can check yours and take it apart, to see what it does. Naturally there are many special codes used by the modem for other things like changing the modem volume, (often L1, L2 and L3 are used for low to high).
Many special settings can be found in your modem manual, but perhaps this story will make that information somewhat simpler to read. My thanks to the folks at GVC, Hayes, Boca, Supra and Galacticomm for teaching me much of what I know about the subject.
If you would like to have computer questions answered, please send them to me by e-mail at Kansas City Mail Online or by the Internet: graeme@kcmo.metrobbs.com. The e-mail impaired can reach me by fax at 816-252-5545 or phone at 816-252-4080.
Graeme Gibson, C.D.P. is the Service Director of Computer Training Corporation and author of ``How to Build a Clone Computer'' and ``The Computer Repair Handbook.'' A former NASA programmer, he has worked in the computer field since 1972. His weekly TV show Computers Today is distributed locally by American Cablevision and Tele-Cable. Check with your cable company for additional times and channels.
Write me at graeme@kcmo.com or for the e-mail impaired, fax 816-252-5545 with questions or comments.
Graeme Gibson, C.D.P. is the Service Director of Computer Training Corporation and author of ``How to Build a Clone Computer'' and ``The Subliminal Software Series.'' A former NASA programmer, he has worked in the computer field since 1972. His weekly TV show, "Computers Today," is distributed locally by American Cablevision and Tele-Cable.
copyright Graeme Gibson, C.D.P. 1996
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