ATARI JOYSTICK INTERFACE

AGF has now modified its joystick interface to accept standard Atari joysticks. The interface allows you to simulate the cursor keys on a Spectrum or ZX-81 plus second set of keys for a second player.

Much software uses cursor keys and AGF provides some demonstration software with each unit so you can look for the cheapest joysticks which can be used on Ataris - there is a range from Le Stick to Competition Pro.

AGF sells the interface at £20 and the address is 26 Van Gough Place, Bognor Regis, West Sussex PO22 9BY. You should indicate which machine you have.

AIMING TO SPEED THE RESPONSE

Stephen Adams looks at the wide range of joysticks that are now the market.

Joysticks are a favourite weapon against space invaders, pirates and in other fighting games. They are also very useful for flight simulation, maze games like Mazog for the ZX-81 or Escape for the Spectrum. That is because they speed the response to the games by up to 300 percent and if the games have been written to obey joysticks, the response to the keyboard has probably made the game run more slowly.

Most work on one of two principles, the commonest being the switched type like the Atari joystick. The other is the proportional joystick, which instead of just indicating the direction of the joystick also sends back a report on its exact position. It does so by giving an X/Y value for the position of the stick in the vertical and horizontal directions. You can write software for those joysticks but no commercial software uses them.

The Atari joystick set a standard by being the first to be used on a video game and since then the style has changed but the connections to the game have not. The Atari joystick has a 9-pin "D" type socket on the end of it which has five pins at the top and four pins at the bottom. They are numbered from one to nine, starting at the top right-hand side - looking at the plug - and only pins 1-4, 6 and 8 are connected. Those pins are connected to five switches in the joystick, one side of the switch being connected to a numbered socket, and the other being connected to a common point, which is connected to pin on the socket.

Operating the joystick in any of the four directions makes that switch operate, connecting the common pin to the socket pin of that switch. The fifth switch is the fire button. Thus only one switch can be operated at a time, plus the fire button. That kind of switch cannot be used directly in place of the keyboard switches, as all the switches are connected together. Therefore an interface has to be used to connect the joystick to the Spectrum without damaging it.

The interfaces are of various kinds but a standard seems to have been set by Kempston, which contacted software companies before it launched its joystick to pursuade them that there should be a standard way of using a joystick on a Spectrum.

That standard way of working has now been written into some of the software by mos of the big companies as an alternative to using the Sinclair keyboard.

The software is easier to write if you have only one address to look at or to control. It is also not difficult in machine code to take one byte from an address and check that a switch has operated. It is much easier than scanning the entire keyboard for several different keys.

The address the Kempstori uses is very simple; it requires only bit A6 to be low using anIN instruction to operate the chip. Address 31 is used to read the value of the joystick. The joystick switches each operate one bit of the binary data returned from the port and as the Kempston Competition Pro joystick allows you to operate two switches directly instead of one - allowing you to go in diagonal directions as well - it is very useful. Only five of the bits are thus used and all the rest are set to 0. If one of the joystick switches is operated, that bit changes to a binary 1 and the number returned will be greater than zero.

The AGF Interface II allows you to simulate a set of keys on the keyboard but they are fixed to the cursor keys and use 0 for the fire button. It also allows you to use other devices on the back of the joystick and is available in ZX-81 and Spectrum versions.

Unlike the Kempston joystick, which works on both the ZX-81 and Spectrum with the appropriate software, keyboard interfaces for the Spectrum cannot be transferred to the ZX-81 as not only is the edge connector too big - 28 ways instead of the 23 of the ZX-81 - but the expansion port has different connections.

The Protek is also a cursor-type interface but like most of the interfaces reviewed has no PCB edge to which to connect anything else like a sound board.

The Jiles Electronics interface is a three-way, bare-board device which can he made to look like that from Kempston, a cursor-controlled joystick, or to work Psion programs. The selection is via two little pegs and is probably the cheapest solution to fitting joysticks, at £13.95.

The Sinclair joystick port in Interface Two operates either the first five or the last five of the number keys. The only software which works with the system is that from Sinclair or Psion.

Soundboards like the Fuller Box and the ZXM from Timedata also have joystick interfaces but use different addresses for them.

Programmable joystick interfaces have also begun to appear for the Spectrum which allow you to program the positions of the joystick to operate different keys on the keyboard. That allows you to operate it with any software, whether it be designed for the joystick or not.

The simplest to understand is the Pickard controller, a plastic box on which there are 40 sockets, one for each key on the keyboard. Five jack plugs, the same type as the cassette leads, are used to program the five positions of the joystick by plugging them into the appropriate sockets for the game.

At no time is the keyboard disabled. The connection to the joystick is via an Atari socket on the side and the connection to the computer is made by plugging-in plugs to the keyboard sockets inside the case. The power is obtained by plugging the power supply into the unit and then a flying lead is plugged into the computer power socket. It is a very simple and inexpensive way of doing the job and will work for the ZX81 or Spectrum.

The AGF version also programs it manually by using a set of crocodile clips, one for each data line and one for each address line. It now seems a complicated way of doing things, as it is not as easy to understand as the Pickard, but it does not involve entering the computer. A set of cards is provided to mark the positions of the clips for each game, which seems to prove the point. The unit also tends to be unstable and programming it during a game can crash the system.

Cambridge Computing and Stone- chip have employed a different method to program the joystick. They have used 1K of RAM to store the positions of the keys where the joystick should operate. In the Stonechip design you can even have the diagonals operating different keys, giving nine positions.

The Stonechip is also the easiest to operate and has the advantage over the Cambridge in that it will also operate the Microdrive interface, Interface One. To use it all you have to do is push a three-position switch to PROGRAM on the front of the unit and, while holding down the key for that position, operate the joystick. A quick flick is all that is required for each position of the joystick. Then move the switch to NORMAL and LOAD the game.

To use the joystick just switch it to PLAY and the game will respond to the joystick. The review model also disabled the keyboard when in use but the company says a small modification will be done to all the current units to prevent that and will be informing all customers so far as to when to return units for free modification.

The Cambridge unit requires you to LOAD a tape first, which takes you through a menu to program the joystick. If you touch the joystick while LOADing the program, it crashes. It also appears to crash after programming the joystick completely as it NEWs itself to be ready for the next program and that is not mentioned in the instructions - but the joystick still works.

The joystick settings can also be viewed and recorded on tape. The menu program still has to be LOADed first. It has also a rear edge connector so that other things can be plugged-in. The interface is intended to work with the joystick which accompanies it but can still be purchased separately if you want to use an Atari joystick.

The advantage of using your own is that you not only have an eight-position joystick but two independent fire buttons for games at a cheaper price than Atari. Cambridge says it will change software when it can obtain a Microdrive on which to test it.

Electrotech also uses the same system to program its joystick but its interface board is uncased and will work only with its joystick console. The console contains a four-position joystick and three large 1in. fire buttons and looks as if it should belong in an arcade game. It is very robust but costs at least half as much again as the other two.

Joysticks tend to be personal things, so I asked a few friends at a computer club and my children for their options on the range available. The result is clearly for the Kraft joystick, with Cambridge Computing second with its two fire buttons. The Kempston Competition Pro joystick is a good all-rounder with its eight positions.

The others go to show that an increase in price does not always provide easier control. The Jiles Electronic joystick is probably the least helpful, as its stick becomes more like a flexible toy in use. The Atari shows how much joysticks have developed, as it now seems very stiff and unresponsive compared to the newer types.

INTERFACITS - JOYSTICK INTERFACING INVESTIGATED

A comprehensive round up of the units available - checked out by our team of reviewers.

One of the first add-ons that a computer owner may contemplate buying is a joystick of some kind. The increase in control that this provides is of obvious benefit to the dedicated games player. In addition it is becoming increasingly necessary for some of the complex graphics packages that are appearing for the Spectrum. However if you have not yet taken the plunge and are now contemplating the purchase of some form of controller you have a difficult choice ahead of you. In essence, most of the actual joysticks are very similar, and your eventual purchase will be based upon personal preferences for shape, size, ease of use etc., but the biggest decision to make will be that concerning the vital link between your joystick and the computer i.e. the INTERFACE.

Interfaces allow the use of joysticks with compatible software, and although there is a great variety of material available for use with all the more common interfaces no single one will give you control over every game, unless, of course you opt for a PROGRAMMABLE INTERFACE. These claim to give you joystick compatibility with ALL software.

AGF have two joystick interfaces on the market at the moment - one programmable and the other not. Interface II is the non-programmable one, but there are versions for both the ZX81 and the Spectrum.

The interface will accept a wide range of joysticks including Atari, Starfighter, Le Stick etc. and has facility for a second joystick to be used. There isn't much to it in the way of hardware, just a few plugs and sockets and six chips. I noticed they have rubbed off the numbers on the chips to deter people making their own, but at £9.95 it's not worth the bother.

The interface just clips on the back of your computer and has a rear extension for more add-ons. With a joystick plugged straight in it will mimic keys 5, 6, 7, 8 and 0 and the second port will give you T, Y, U, I and P.

To convert games that do not use these keys, you will have to purchase AGF's software and you have a choice of two cassettes. Tape one will convert Arcadia, Schizoids, Hungry Horace, Horace goes Skiing, Spectres, Penetrator and tape two converts Centipede, Planetoids, Jet Pac, PSSST, 3D Combat Zone and Invaders.

After you have loaded the cassette it will ask you which game you would like to play and after running the tape further it will automatically find the corresponding software to convert that game and tells you when to load your game.

On the inlay, it lists the games you can use the interface with. I would have thought it would have been better to list the key operations as well so that it would be easy to find what other games you could play with it.

You can buy the interface, software and joystick direct from AGF if you cannot find it at your local store. Cassettes are £4.95.

It is a slightly 'Heath Robinson' way of connecting a joystick but it is cheap.