By John Ilsley for the Master 128 This article explains the differencebetween ROM and RAM. How this appearson a Master. How you have to take thecomputer to bits to change between thetwo. Then how you can carry out a minorop on your pride and joy to enable youto toggle between RAM and ROM with theflip of a switch instead. What is RAM and ROM? There are 4*16k banks of sideways RAMin your Master 128 this RAM can be usedfor programs that you load in fromdisc, sound samples for example whichneed all the memory they can get. Whenyou switch the computer off, all thedata is lost and you have to load itall in from disc again the next timeyou want it. These banks can also be 2*32k ROMS butnot at the same time as being 4 banksof RAM!. The ROM sockets are located at theright hand side of the Master circuitboard. You may plug ROMs into thesesockets. ROMs such as Printmaster orPASCAL. When you switch the computeron, the program which is "burnt" ontothe chip is already installed and readyto run as soon as you issue the correct* command. You may put your own programs onto yourown ROM but this needs an EPROM andEPROM programmer. There have beenadvertisements in this mag, peopleoffering to program EPROMs for you. There are also two slots at the righthand side of the Master just above thenumeric keypad. You can plug acartridge containing ROMS into theseslots How does ROM/RAM appear on a Master? Type *ROMS RETURN You will see a list of all the standardROMs fitted and their ROM slot numbers.Look at slots 5,6,7 and 8. If there isa ? next to the number, then this slotis RAM. If there is the name of a ROMthere, then you have ROM fitted. If you buy a ROM and want to fit itinto one of the slots on the circuitboard, you have to do 2 things. 1. Take your computer to bits and plugthe ROM into one of the empty sockets.2. Change a hardware link near the ROMto tell the computer to recognise theROM instead of giving you RAM. If you then need RAM at a later stagefor playing sound samples for instance,you must change this link back. Thereis no need to actually remove the ROM,but it still involves removing thecover of your computer each time youneed to change the link. There are 2 links. Labelled on thecircuit board as LK18 and LK19. Theyare tiny bits of plastic which pushonto two of the three pegs of eachsocket. If a link is fitted to the EAST(the right hand 2 pegs) it tells thecomputer to recognise a 32K ROM. If alink is fitted to the WEST, it tellsthe computer to recognise two 16K RAMslots. Link 18 is responsible for switchingslots 4 and 5. Link 19 is responsible for switchingslots 6 and 7. How can you avoid moving the link? This project adds a switch onto link 19so that slots 6 and 7 can be toggledbetween ROM and RAM with the flip of aswitch. This can also be carried outon link 18 in the same manner, insteadof or as well as link 19. Let's take a look at the inside of a Master: West. East. link 19 ] slot 6&7 link 18 ] slot 4&5 Keyboard Speaker connectors ^ ^ Assembly. A Minor op on your pride and joy. Two major points to note: 1. If you are not sure that you cansolder or put a switch in, then don'ttry as you may cause serious damageto yourself and/or the computer.Instead, take it and these instructionsto a qualified engineer. 2. This project is for the MASTER 128ONLY! Neither I or 8BIT will acceptresponsibility for any damage you maydo to yourself or your computer whilstfollowing these instructions. I repeat,if you are not certain of what you aredoing, either ask someone who knows orquit! You will need: One miniature SPDT toggle switch. One piece of insulated wire, about 3ft in length. Start by: Cutting the wire into three equallengths. Switch off the computer and remove thefour fixing screws on the underside. The cover should now lift off. With the keyboard facing you, removethe screws that hold the keyboard inplace, unplug the two ribbon connectorsthen lift the keyboard out and put itto one side. You may like to clean thekeyboard now you've removed it. Lift the speaker case and unplug thespeaker. Put it to one side. Cap, facemask and rubber gloves. Scalpel in one hand, resus team at the ready. Commence the op! Take each piece of wire and remove 5mmof the outer insulation from each end.Put a small amount of solder onto theend of each wire. Put a small amount of solder onto eachof the three pins of the switch. Remove the link from link 19 and put asmall amount of solder onto each ofthe three pins of link 19. Now decide where to mount the switch onthe case. Drill a small hole largeenough to take the threads of theswitch. I have mounted mine on thebottom right hand corner of the lowercase since this has a large accessiblearea capable of taking the switch. When you have made the hole, take theswitch and the three pieces of wire andsolder one wire to each of the pins onthe switch. As you have already tinnedthe parts to be soldered, the rest ofthe soldering should be quite simple. The three remaining wire ends go tolink19. Solder the wire that comesfrom the centre pin of the switch tothe centre pin of link19. The other twowires go to either of the two remainingpins of link19. Place the wires so theywon't get trapped anywhere be verycareful not to bend the pins togetheror to join them with solder. Carefully put the switch through thehole and secure it. Make sure that all your connections arecorrect. Plug the speaker back in. Being carefulto route the wires correctly. Put the keyboard in place and push inthe keyboard ribbon connectors. Make sure there are no tools or bits ofsolder or wire loose in the computer,They could cause a short circuit. Replace the cover. Power up. You should get the normalstartup sound and message. If you donot, then switch off immediately andcheck all your connections. If you hadno sound, check the speaker connectionvery carefully. If you had any otherproblems, remove the project from yourmachine and contact me! If the power up was normal, test outthe project by loading files intosideways RAM banks 6 and 7: *SRLOAD <filename> 8000 (6 to 7) Q Then flip the switch and repeat. Inthis way you will find out which switchposition gives you 1*64K ROM bank inslots 6 and 7 with the ROM enabled andwhich switch position gives you 2*16KRAM banks in slots 6 and 7 withsideways RAM enabled. You can flip between ROM and RAM atwill. You will find that the RAM imagesare still there even after changingfrom RAM to ROM and back again. As I mentioned earlier, this projectwas for link 19 only. If you want to dothe same with link 18 the procedure isexactly the same. You will then be ableto toggle slots 4 and 5 between ROM andRAM. I intend to submit more articles likethis in the near future. I have oneplanned for the good old BBC B, aproject to freeze the computer. Has anyone any ideas for a project thatthey would like me to attempt on my BBCor Master? Happy soldering....!