Printers usually plug into a parallel port and mice use serial ports (that is, if they can't find a hole big enough to get inside and chew up the wires!) The one that we'll be using is the serial port.
The computer you're using is almost certain to have a serial port, however if it doesn't you can buy a "serial card" quite cheaply and plug it into one of the connectors on the mother board. If you install one of these you will have to configure it in a way that will work with your computer. The supplier can explain this. It can generally be plugged into any vacant slot on the mother board.
Serial ports are usually either 25 pin or 9 pin male connectors. Parallel ports are usually 25 pin female connectors. So to connect something to a serial port, you'll need a cable with a 25 pin (or 9 pin) female plug on one end and the correct plug for whatever you're connecting to it on the other end.
As explained in chapter three, the signals that computers use won't travel very far down wires and therefore have to be converted into audio signals, which do travel well through long wires. This is what a modem does.
"Modem" is short for MOdulator/DEModulator. Modulation is the process of converting digital signals into sound signals.
As well as converting the data into a form in which it can be sent down a phone line, modern modems are able to dial phone numbers and answer incoming calls automatically.
There are two types of modem: internal and external. They both do exactly the same thing. The difference is that one goes inside the computer - it is in the form of an option card and plugs into the mother board - and the other is in a box of its own and must be connected to a serial port via a modem cable.
Both types of modem have their advantages. Internal ones are considerably cheaper and don't require a separate serial card, however they can't necessarily be used with other types of computer. External modems really only have the advantage of being compatible with all types of computers (given the right cable) and they can be easily disconnected and used somewhere else. Either way, they are easy to install and operate.
A null modem is simply a cable that's configured in a way that connects the serial ports of the two computers together in the right way for them to work properly. (The connector on a modem is wired up so that all the pins on the computer's serial port are connected to the same pins on the modem. This won't work between two computers.)
At the moment, we'll only consider calling out to another computer. The job of taking incoming calls usually falls to Bulletin Board software and we'll talk about that later.
So, say you want to use your computer and phone line to call up a bulletin board. What do you have to do to get it happening?
Firstly, the software must be configured to do what you want it to. This is usually not very difficult. The comms prog will have a setup menu to do it. All software packages have a default way of setting themselves up and this is usually good enough to start with. When you get familiar with it, you may want to change some of the ways it's set up, but it probably won't be totally necessary.
One thing you must set up though, is the way the software talks to the modem. Firstly, you must make sure it's using the right communications port. The computer has its internal ways of identifying different ports and it's possible to have at least four different serial ports. When the serial card was installed, it would have been configured to be a particular port. There's a good chance that this will be COM1, but not necessarily. You must either know this or fuck around trying different things till it works!
Once you've got the right COM port, you have to set the speed that it's going to talk to the modem at. For this, you'll need the modem manual. It will probably be best to set it at the modem's maximum speed, however, with some modems, it's better to have it a lot faster than that.
Now what exactly do we mean by speed? Basically, it's how many BITs are transmitted in a second. But it's not exactly that! Do you really want to know?
Well, i'd better tell you anyway...
Data transmission speed is measured in bits per second (bps). Another word for bps is 'baud'. 1 baud = 1bps. However, it's not quite that simple as the communications hardware needs to use some of those bits for its own internal control purposes. Therefore if two computers are talking at 2400 baud, you won't get 2400 bits per second of usable data. What you will get depends on what's called the 'protocol' you're using. Protocol is the way the computers control the communication between them and check for errors etc.
With most of the communication we're likely to be involved in, the thing that interests us most is how many characters we're getting per second. And even this isn't really essential knowledge. However, it helps to be familiar with this stuff so you know what other people are on about when they refer to it.
When you set up your communications software, you'll see a section where you can specify 'parity', 'data bits' and 'stop bits'. These will probably be set to 'N', '8' and '1' by default and this is what we're likely to use all the time.
Parity is a primitive form of error checking which more or less comes from adding up all the bits in a byte in a way that leaves you with just one bit (0 or 1). This is done before the data's sent and then again by the computer receiving it and the parity bits should come out the same both times. However this is a pretty unreliable form of error checking and it's rarely used nowadays. The 'N' stands for 'none' (i.e. no parity checking). The other possibilities are Odd, Even, Mark and Space, but if you're interested in them you can find out about them yourself!
The '8' stands for 8 data bits to a byte. The other possibility is 7 - which leaves one spare bit for parity. This is why the ASCII code is 7 bits (to leave a spare bit for parity - which isn't used much anymore, what a waste!)
The '1' means 1 stop bit. Stop bits are what the hardware uses to synchronize communications with the other computer (or with the modem). The alternative is 2. As well as either one or two stop bits being added to the end of each byte, one 'start bit' is added at the beginning for the same reason.
So obviously, for two computers to talk properly, they must both use the same data format (e.g. N.8.1).
How does this affect transmission speeds? Well, if you've got 8 bits of data you want and 2 bits that the computer needs (1 start & 1 stop bit), you're not going to get 2400 usable bits per second out of 2400 baud. What you do get is 1920 bps, which is 240 characters per second (cps), rather than the 300 cps you might expect. Normally, the baud rate is used to refer to how fast data is going down the line, while bps refers to how many usable bits you're getting.
What i've said above is true for simple computer-computer or computer-modem communication but isn't strictly true when it comes to modems. The baud rate of a modem-modem connection is a totally different thing to the bit per second rate. This is because, baud really refers to how often the signal can change and every signal change in a modem running at over 300 bps signifies more than one bit. (Erm... I don't want to get too technical about this, but i feel it does need a bit of clarification.)
For example, at some speeds a modem will communicate four bits with one signal change. That means each baud = 4 bps. Etc etc...
As i said, you really don't need to use this knowledge, but it does come up quite often in discussions on BBSs, and it also helps clarify some of the settings of your comms software. Don't worry if you don't fully understand it.
Most modems are what's known as "Hayes compatible". This means they accept commands from the computer in a standard form. You'll need to refer to your modem manual to find out about the commands you need to get it working in the right way.
Some simple options include whether or not the modem automatically answers incoming calls, whether the speaker in the modem lets you hear it dialling or not, whether it uses tone or pulse dialling, etc. There will also be a command for it to dial a number.
These commands take the form of 'AT' at the beginning, followed by letter and number codes for the functions it is to perform.
For example, the command to dial 03-123 4567 would be:
ATD031234567<CR>
The <CR> means carriage return and is represented in different ways by different comms s/ware. check the manual on this. However, your comms s/ware will almost certainly allow you to dial a number more easily than that.
TELIX is the name of the comms program i use most and it has a phone directory which you add numbers to with simple commands. You can then dial them by placing a cursor at the entry you want and typing 'd'.
But you may have trouble with the modem not working properly. This usually comes from it not being 'initialized' correctly.
Initialization is something the comms s/ware does when you first start it up. Amongst other things, it sends a command string to the modem to configure it correctly.
The comms s/ware will come with a default initialization string ('string' just means a group of characters, e.g.: ATD031234567).
The default initialization string may work, but it probably won't as all types of modems seem to be slightly different in the way they're set up. If you have problems, you'll have to read your modem manual and either try and find an initialization string the manufacturers reccommend or make your own one from the information in the manual. This is always one of the first things to check if your modem is doing weird things.
You can set up the initialization string in the comms program's setup menu.
The obvious way to test it all out is to call up another computer and use it to talk to that computer with. There are lots of public access computer systems, known as Bulletin Board Systems (BBSs). These are mainly run by single individuals or small groups as a community service. Access is generally free and various forms of participation are supported.
The main functions of BBSs are message exchange, file exchange and game playing. For a fuller description of BBSs check out the chapter on that subject in part two.
So the best way to check out your comms setup is calling up a BBS. How you find the phone number of your first BBS, i'm buggered if i know! Once you've found one, you can usually find all the rest in one way or another. In australia, there's a national BBS list which is circulated amongst BBSs, but i don't know how you'd get it without already knowing one. Also, most BBSs carry a few numbers of other BBSs of a similar mentality. Occasionally you'll see an article in a newspaper on the subject which will have a few numbers and i've never looked at a computer magazine, but i guess they probably have that sort of thing too.
Once you've got your BBS phone number, you can enter it in the dialling directory of your comms program. And then try dialling it.
And...
Well, there could be several reasons for that screenfull of meaningless garbage - like the protocol's not set right (N,8,1, etc), modem speed's wrong, computer speed's wrong, serial port card's fucked out......
What?! You haven't got a screenfull of meaningless garbage?!?! Far out! Well, there ya go, life ain't all bad is it?
So what will you see when your computer's connected to the BBS?
Sometimes, nothing at all for a while, as the BBS computer loads up its comms s/ware and sorts itself out. If it seems to be taking a long time to happen, hitting <ENTER> or <ESC> once or twice might spark it off.
And then you get maybe a title screen with the BBS name etc, or maybe just a prompt asking for your name (some systems ask for LOGIN: - this is the same thing).
When you enter your name, the system will recognize that it doesn't know you (on your first call, that is) and ask you a few questions. What these are depends on the individual sysop (the person that runs the BBS - short for SYStems OPerator). But one thing it will ask you to do is choose a password. This is a word you'll use every time you log on to (call up) this BBS so it knows you're really who you say you are. It should be at least 6 characters and something that won't be an easy guess for someone else. You'll be able to change this any time you feel like it.
You'll also probably get asked questions on the setup of your computer, like screen size etc. Usually, hitting <ENTER> will select the default value and this will be right - again, you can change all this sort of stuff later.
Mostly, finding your way around a BBS is easy. You should be presented with menus and clear choices all the way and maybe even "help" commands for when you get stuck.
The best start is to read through some of the messages on the first message area you come to. Depending on the particular software the BBS is using, this will be simple and straightforward, or slightly confusing. Either way, it just takes a bit of getting used to. Don't panic! It will all become clear in the end! Maybe!
One command that needs explaining is the 'Logoff' command. This means "end this call to this BBS".
If the first bulletin board you call isn't very interesting, that's normal. There's lots of them, they all cater for different types of people and there's always one which you'll find interesting. Just keep groping around and you'll find it.
After your session on the BBS, check your modem has hung up the phone right. Sometimes they don't - it's another case of getting it configured right...
So if everything went right, you're ready to take on the freaky world of computer communications. But watch out! BBSing can be addictive. Some people spend hours every day reading and writing messages, playing games etc on BBSs...
click here to go to chapter five