★ HARDWARE ★ MONTAGES ★ START W.A.R.T.S (AMSTRAD ACTION)|Amstrad Action) ★ |
| Start W.A.R.T.S (Amstrad Action) | Hardware Montages |
Well, not AA as such. More PHIL CRAVEN, W.A.R.T.S. and all, with a piece evidently written under the influence of too much cough mixture. In recent months there's been a lot of publicity about computer viruses. What with the April Fool's day bomb types, the general purpose screw-up-your-programs types and the dangerous invasion of the NASA computers, all working on other kinds of machines, we CPC owners have led a charmed existence. So far none of these pesky little viruses has seen fit to infect Amstrad's finest. Until now, that is. For your correspondent has uncovered what is possibly the most insidious and deadly virus of them all... WARTS. This lethal menace kills all external ROMs -dead. Fortunately no virus, including WARTS, is invincible. After much brainstorming, many sleepless nights and the ed's signature on a commissions contract (news to me -ed.), I can announce that a 12 month subscription to Amstrad Action works as the perfect antidote to WARTS.
Seriously though, folks Since most external roms allocate an area of memory for their own use, some more than others, and reduce the free memory pool, some software is prevented from running when too many of them are attached. Often the software checks the space available and, if there isn't enough, it comes back with a pesky "Turn some ROMs off' type message. Others simply crash. Either way it becomes necessary to either switch the ROMs off or unplug the board.
Only the Microgenic board has a switch to do this. Some of the others have tiny individual switches for each ROM which are not exactly easy to flick off, especially if the board is boxed, while the rest have no switches at all. Unplugging the board is just as inconvenient. Hence WARTS, which is clearly a tortuous acronym for "Whizzo All ROMs Toggle Switch." It allows you to turn off all external ROMs however many boards are connected - but it wont affect the internal system ROM. The parts cost a mere £4 and the project takes just a few minutes to make. And this is what you do... Whenever the CPC accesses any ROM it sends the ROMEN signal, pin 42 of the 50 way expansion connector, low. All ROMboards use this signal to determine whether or not the address and data on the buses are intended for a ROM. If they are, then the particular ROM is enabled. It follows that no ROM can be enabled where ROMEN is not allowed to go. If we prevent it from going past the WARTS and out to any ROMboards then the external ROMs cannot be enabled. And that's precisely what we do. ROMEN is intercepted and fed to the pole or centre of the switch while the switch position feeds it on out to the ROMboards or leaves it hanging in the air. A pull up resistor is included to improve reliability.
Making it The 50 way edge connector has a locating key and only fits the CPC one way round. Be sure to get it the right way. In your User Instructions, chapter 7 page 40, you will find the pin connections of the expansion socket. Bend the ROMEN pin 42 of the edge connector right down flat between pins 41 and 39 so that it touches neither. Squeeze the rest of the two rows close together. Put the through connector between them, making sure that its locating 'slot' is also the right way round, and solder the rest of the edge connector's pins to it. Don't solder the pin you have bent down. Leave about a 3/16" gap between the edge and through connectors. Strip about 3/16" of the insulation from each end of the wire, solder one end to the centre pin of the switch and bend the two outer pins slightly away from the centre. Now solder the resistor as closely as possible to one side pin of the switch. Lower the switch to just above the connector assembly so that the wire passes between 37/38 and 35/36 and the resistor pin is approximately above pin 33. The other end of the resistor is soldered to pin 27 of the edge connector and the wire to pin 42 of the through connector. Cut them to size and solder accordingly. Solder the bent pin 42 to the other side pin of the switch. If no accidental connections have been made then the unit will now work and can be tested: but before we finish we must ensure that the bent pin cannot touch any other pins àt a later time. Figure 2: the circuit diagram >> For this I used woodworking adhesive which I squeezed between the pins having made sure they were correctly positioned. It has the advantage of drying rigid, and also adds to the stability of the switch. Further stability can be gained, after testing, by adding more adhesive. Bits ROMs reserve their memory on power up or reset and simply switching them off does not release the memory. A reset must also be performed. Similarly, switching them on doesn't cause them to grab what memory they need. Again it must be a reset after switching. Any ROMs that are closer to the computer than the switch will not be affected so, if you want to leave the silicon disk working, for instance, put the switch outside it. All ROMs outside the switch will be affected and this includes the disk drive ROM in the 464's disc interface unit. Sorry folks, it's not my fault they didn't put a through connector on it and it has to be the last one out!
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