|★ HARDWARE ★ PERIPHERIQUES CPC - MODEMS ★ PROTEK: 1200 MODEM INTERFACE PACK ★|
|Modem - Protek - 1200 Modem Interface Pack||Hardware Peripheriques Cpc - Modems|
There are three things to bear in mind when connecting a CPC464 with a telephone line.
To answer these questions in order:
There are several types of computers which can be called up with a modem. The simplest is just another user. For this all you need is the right modem and software. Next up the scale is the bulletin board. This is a database run on a small computer, usually by a private individual. As a rule only one person at a time can be connected to a bulletin board. The commonest type of database for users to log into is the mainframe database. Of these, Prestel is the most important.
A serial interface runs at a certain speed. It is possible to build an interface which can run at all the speeds you are ever likely to need, however this is an expensive solution. There are two main speeds required for connecting to other computers. The first is 1200/75 baud. This means that your computer receives information at 1200 bits per second and sends it at 75 bits per second. This is ideal for logging into a database but a bit slow for user to user. For bulletin boards it is more common to use 300/300. Both these speeds are used "Full duplex' which means that the computers at both ends can 'talk' and 'listen' simultaneously. For user-to-user applications, it is possible to take it in turns to talk and listen. This is called 'half duplex' and is usually done at 1200/1200. For all these speeds, you need a modem to match, and to be connected to a distant, or host, computer which is talking at the right baud rate.
The software is even more specialised. Not only does it need to run at the right speeds but it also needs to know the protocol for sending characters. For systems like Prestel, a kind of software known as viewdata is required. For logging into bulletin boards or communicating with business type services you need 'glass teletype' software. Again you need to decide before you buy; the software can make or break a package.
Finally the modem. The first distinction to be made is between the acoustic coupler and the hardwired modem. A coupler fits over the mouthpiece and earpiece of a normal telephone. A hardwired modem plugs into the wall in the same way as a modern telephone. Acoustic couplers are usually battery powered, whilst hardwired modems tend to run off the mains. Since all you need to use an acoustic modem is a standard 'phone, it scores in being portable. However any noise in the room can cause the sounds being transmitted to be garbled. This makes a hardwired modem more reliable.
Whatever type of modem you buy, you will need it to run at the right speeds. More expensive modems are switchable and allow you to dial up a selection of hosts. These multi-standard modems are nearly always hardwired since the physical coupling of the acoustic modems forms part" of the frequency dependent 'circuit' that is specific to one modem speed.
How does the Protek 1200 and Amstrad serial interface package rate in this field of choice?
For a start it will run at 1200/75 and 1200/1200 half duplex. This means that it can be used to communicate with Prestel and as a user-to-user system. There are very few bulletin boards which run at 1200/75, a notable exception being VISA which is on between 8pm and 11pm every night on 01-959-7098. Like Prestel VISA uses viewdata format.
The serial interface is small and neat. It is well constructed with a minimum of components. A cable joins the interface to the modem. There are two flaws in the design of the interface for the 464- both to do with the connectors. The first is that there is no locating lug in the socket which plugs onto the back of the computer. Because of this it is easy to plug the interface in and then find that the screen goes awry when you turn the power on. Secondly, the socket at the back of the interface should allow you to connect any other additional accessory; however, the disc interface will not fit on, partly because the box is too big and the connector does not protrude, but mainly because the printed circuit board at the interface end is too wide to fit into the slot in the disc interface box. I understand that Protek intend to rectify this soon. The viewdata software is adequate. Because Prestel uses a weird screen format, it is not possible for the CPC464/664 to simulate it completely. Prestel needs eight colours and forty columns for text. The Protek software provides four colours. Red, blue, black and white. For this reason some of the frames look a bit anaemic, but this is a fair compromise. Not all dynamic frames work properly, the colour very often leaves a trace which should disappear. There are options to save a screen to tape and to print a frame. It is a great shame that a disc cannot be used (yet), as this will make it far cheaper to save frames.
Before you log in, you have to type your ID. This means that anyone looking over your shoulder gets a good look at this supposedly secret information. Perhaps the most annoying omission is the lack of a cursor when using the mailbox or response frame pages. Further, there is no 'reveal'option, but despite all this, the combination of interface and software is a bargain at £29.
The modem itself is of the acoustic type, and it fits the standard telephone well. There are two sets of batteries to be fitted into the modem and as you join the telephone to the handset the lids on the battery compartments tend to open. When the batteries are new the modem performs very well, but as they start to run down, the amount of 'line noise' (corrupted information) increases - so stick to alkaline types. There is a three way switch to set the modem to 1200/75, 1200/1200 or OFF, and an earphone socket. Although not spectacular, the modem is a good solid device with BT approval. The price tag of £59.95 for the modem is quite reasonable for a BT approved device, and what's more, it's available! All in all a neat little package, and for less than £100, it is a cheap way to get into the world of communications.