TELL-A -WHAT?

BY[ DWIGHT CAMPBELL

From Memphis East Commodore Organization

 One of the technical marvels of today is telecommunication,  the overall process of connecting computers together . If you get yourself a modem and the appropriate terminal software ( as in " computer terminal ", not the medical sense ), you can hook up your touchtone phone to the computer and begin transmitting and / or recieving any of a vast offering of services too numerous to mention in a short article . 
 Telecommunication allows users to overcome limitations of time,  location,  and for the most part,  incompatibilty between different makes or types of computer systems . 

The exchange of hard copy,  or file documents is less than desirable since most computers have incompatible disk formats . ( an Apple,  TI,  Atari,  IBM,  etc . disk will not run on a Commodore ) Mailing incompatible disks is slow and the risk of loss or damage is great . Mailing a hard copy code printout requires re - typing and change of code and is too time consuming.  

Telecommunication overcomes most of these incompatibility problems among brands / types of computers . A Commodore can communicate with a behemoth mainframe or talk to a TI . The secret of this compatibility are established standards of communication . ALL computers operate by using " bits " or BInary digiTS which literally,  are on / off switchs built into the chips of the computer . Eight of these digits makeup a byte . A byte contains two to the power eight or 256 possible numeric combinations . When a key is struck on the keyboard,  a specific combination of these 256 possible combinations is stored into the computer . These combinations are defined byN an American standard for all keyboard characters,  ASCII ( pronounced AS - KEY ). The computer can communicate with other,  different computers due to the fact that all computers generate the same ASCII characters for text . That is,  typing the letter Z on an Atari will generate the letter Z on a Commodore because o the exchange of ASCII code . Commodore is one of the few machines which utilizes unique ASCII code for graphics,  thus the incompatiblity of graphics characters between other manufacturers . 
 
In order for machines to communicate,  there has to be a physical link . You can ' t just connect a wire between two computers and expect them to " talk "! To accomplish satisfactory communications between computers,  they must first have a common language . Although ASCII is technically forming the words,  the ASCII codes originating in one computer must be converted for transmission to the other computer . Once received, these transmissions must be translated back to an understandable form of ASCII by the receiving computer. 
 
The internal pattern of electrical impulses which travel through a computer can not be sent directly to another computer,  they would not make sense . Therefore,  transmissions must be modulated for travel through the phone lines or cables . The recieving computer must demodulate these signals to translate back to a form it can understand . Data transmission occurs in both directions and each device must MODulate and DEModulate signals . ( thus,  the term MODEM ) 
 
 It is possible to connect certain ~parts~ of two computers ' several feet apart allowing communication between the two successfully . If the information is to be transmitted through a phone system without alteration,  the result would be confusion . This is due to the low output power of the computer ' s signals and also these signals would not be understandable by the phone system nor would it be accurately reproduced at the other end of the phone . In order to translate the computers ' signals into a transmission which can be read at the destination,  a standard system is necessary . The most utilized system currently ( especially for home computers ) is called RS - 232C . RS - 232C is a method of converting computer - generated ASCII code to a form that can be transmitted and accurately received and interpretted . With Commodore computers,  this is the primary ( at the present ) interface used for communication . 

 The RS - 232C standard specifies certain characteristics or Parameters of the signal which is sent through a MODEM . The first standard is BAUD Rate,  or the speed of the modulated signal sent through the transmission line . MODEMS currently available for the C - 64 and C - 128 are 300 or 1200 baud . 1200 baud is of course faster,  but requires " clean " or high quality,  low - noise phone lines to pevent errors during transmission . The higher the baud rate,  the more important the quality of theN phone line . 

 Another parameter or characteristic used to format transferred data is full or half duplex . When data is transferred between computers,  a continuous stream of information can be sent without waiting to see if the message has been recieved at the other end . If both computers operate in this mode it is said to be in half - duplex . In half - duplex,  the transmitting computer can not tell if the recieving computer is acting correctly . Full duplex allows a pause for each computer to answer each transferred character,  or echo . If the echo agrees with the originally transmitted character,  then the next character is transmitted . 
 
In order for the computers to know when each is sending or waiting for
data,  an absolutly essential method to tell the two computers apart is included in all modems ( or may be a feature of the communications software ). This feature is the selectable " originate / answer " mode . If you are placing the call,  your modem should be set in " originate " mode . The answering computer will listen for the " originate " tone
(which is a different pitch from the " answer " tone ) this is how the computers know which is sending and which is recieving . Without two different tones,  the computers would not be able to tell the each apart . Parity and stop bits are terms which are applied to communications also . 

A discussion on these parameters are beyond the scope of this article . As alluded to earlier the communications software allows the computer to convert it ' s own code into a form that can be sent through the modem and then decode data coming into the computer . It allows your computer to act as a remote terminal attached to the other computer regardless if it is a large main frame or your friend across town . 
 
I have only scratched the surface of telecommunications here, but with a
computer and the correct software and hardware,  there is wide world of
experience waiting at the other end of your telephone .