As you might have already read another user E.Clarke is now to handle hardware problems, whether or not the problems will be published as part of techtips or not is at present undecided. As editor of the magazine I personally think that the Tech Tips logo and stylewhich spawned the style of the teletextmagazine should be kept, but with a change of author. I will of course continue to offer helpto people with software problems or programming difficulties. ANDY NIBBS THE BASDUMP PROGRAM: What the Basdump program does is copy any BASIC program currently in memory up into sideways RAM. It can then be recalled from sideways RAM. It can be used to save the BASIC program being worked on whilst doing *FORMAT, *COMPACT and other program deleting star command. Or to keep a backup in memory of a program which keeps damaging itself causing a bad program. It does not ever load programs off discs or make programs runnable by star commands from memory. The article will tell you how to use it. I feel sure I have lost some questions in the time since I last wrote TechtipsIf you have a question hardware or software, don't suffer in silence. Sendyou queries to Duncan. BATTERY BACKUP S Bodman asked Duncan ages ago whether or not I could fit a Battery Backup to a Watford Solderless Rom Board. I have not got one of these boards so I can only discuss battery backup in general in the hope that maybe another members can put the theory into practice. Firstly there are two different types of RAM, Dynamic Ram and Static Ram. Dynamic RAM chips or DRAMs as they are commonly known need their contents to be refreshed continually and any battery backup for DRAMs would need to include refresh circuitry. This would use more power and be more complex. The second consideration is how to actually implement the power changeoverand what backup power source to use. You can either use a battery and if so why not use a Nickel Cadmium (NiCd) rechargable battery and recharge it when the main power is on. Or you can use a capacitor. A capacitor stores electricity and it is possible to buy capacitors designed for this purpose. These are available from Maplin to name but one source. These generally have values of up to 1Fand are intended for use with low powerCMOS static RAM devices and can suppl such a device for 1 or 2 weeks. Maplin stock such capacitors for £4 to £6. The use of battery backup can be simplified by using an automatic switchThe ICL7673 Automatic Battery Backup Switch is designed for battery backup as the name suggests. Vo 1 8 Vp Vs 2 7 NC NOT S 3 6 NOT P GND 4 5 NC The connections 3 and 6 are logic outputs to switch transistors to switchhigh currents. This should not be necessary for battery backup.
Battery backup using rechargeable battery R1 and D1 perform the recharging and should be omitted if the battery is not a NiCd type. The above circuit either provides +5V which is normal for computer power supplies and quite a considerable number of chips in the beeb need +5V. If the circuit is not using the main +5V supply it will provide a 3V or so from the battery. Most CMOS static RAMs will hold their contents at around 2 or 3 volts but if 3 single cell batteries were used the 4½V produced should keep CMOS RAMs happy. The cells used can be AAA types and as such will not take up a huge amount of space. If however, the RAMs are dynamic and refresh circuitry must be driven you probably need a +5V supply for both the circuitry and the RAM itself. The supply must be close to +5V and only deviate by plus or minus 5%. If you do need +5V you might need to use a voltage regulator. All of these things shorten battery life. This is probably my last hardware scripture the rest is up to Mr E.Clarkegood luck to him. All the above parts can be obtained from Maplin. Catalogues are in WHSMITH shops. The ICL7376 costs £1.48. ANDY NIBBS