8-Bit Software Online Conversion

              By John Ilsley for the Master 128 This article explains the difference between ROM and RAM. How this appears on a Master. How you have to take the computer to bits to change between the two. Then how you can carry out a minor op on your pride and joy to enable you to toggle between RAM and ROM with the flip of a switch instead. What is RAM and ROM? There are 4*16k banks of sideways RAM in your Master 128 this RAM can be used for programs that you load in from disc, sound samples for example which need all the memory they can get. When you switch the computer off, all the data is lost and you have to load it all in from disc again the next time you want it. These banks can also be 2*32k ROMS but not at the same time as being 4 banks of RAM!. The ROM sockets are located at the right hand side of the Master circuit board. You may plug ROMs into these sockets. ROMs such as Printmaster or PASCAL. When you switch the computer on, the program which is "burnt" onto the chip is already installed and ready to run as soon as you issue the correct * command. You may put your own programs onto your own ROM but this needs an EPROM and EPROM programmer. There have been advertisements in this mag, people offering to program EPROMs for you. There are also two slots at the right hand side of the Master just above the numeric keypad. You can plug a cartridge containing ROMS into these slots How does ROM/RAM appear on a Master? Type *ROMS RETURN You will see a list of all the standard ROMs fitted and their ROM slot numbers. Look at slots 5,6,7 and 8. If there is a ? next to the number, then this slot is RAM. If there is the name of a ROM there, then you have ROM fitted. If you buy a ROM and want to fit it into one of the slots on the circuit board, you have to do 2 things. 1. Take your computer to bits and plug the ROM into one of the empty sockets. 2. Change a hardware link near the ROM to tell the computer to recognise the ROM instead of giving you RAM. If you then need RAM at a later stage for playing sound samples for instance, you must change this link back. There is no need to actually remove the ROM, but it still involves removing the cover of your computer each time you need to change the link. There are 2 links. Labelled on the circuit board as LK18 and LK19. They are tiny bits of plastic which push onto two of the three pegs of each socket. If a link is fitted to the EAST (the right hand 2 pegs) it tells the computer to recognise a 32K ROM. If a link is fitted to the WEST, it tells the computer to recognise two 16K RAM slots. Link 18 is responsible for switching slots 4 and 5. Link 19 is responsible for switching slots 6 and 7. How can you avoid moving the link? This project adds a switch onto link 19 so that slots 6 and 7 can be toggled between ROM and RAM with the flip of a switch. This can also be carried out on link 18 in the same manner, instead of 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 can solder or put a switch in, then don't try as you may cause serious damage to yourself and/or the computer. Instead, take it and these instructions to a qualified engineer. 2. This project is for the MASTER 128 ONLY! Neither I or 8BIT will accept responsibility for any damage you may do to yourself or your computer whilst following these instructions. I repeat, if you are not certain of what you are doing, either ask someone who knows or quit! You will need: One miniature SPDT toggle switch. One piece of insulated wire, about 3ft in length. Start by: Cutting the wire into three equal lengths. Switch off the computer and remove the four fixing screws on the underside. The cover should now lift off. With the keyboard facing you, remove the screws that hold the keyboard in place, unplug the two ribbon connectors then lift the keyboard out and put it to one side. You may like to clean the keyboard now you've removed it. Lift the speaker case and unplug the speaker. 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 5mm of the outer insulation from each end. Put a small amount of solder onto the end of each wire. Put a small amount of solder onto each of the three pins of the switch. Remove the link from link 19 and put a small amount of solder onto each of the three pins of link 19. Now decide where to mount the switch on the case. Drill a small hole large enough to take the threads of the switch. I have mounted mine on the bottom right hand corner of the lower case since this has a large accessible area capable of taking the switch. When you have made the hole, take the switch and the three pieces of wire and solder one wire to each of the pins on the switch. As you have already tinned the parts to be soldered, the rest of the soldering should be quite simple. The three remaining wire ends go to link19. Solder the wire that comes from the centre pin of the switch to the centre pin of link19. The other two wires go to either of the two remaining pins of link19. Place the wires so they won't get trapped anywhere be very careful not to bend the pins together or to join them with solder. Carefully put the switch through the hole and secure it. Make sure that all your connections are correct. Plug the speaker back in. Being careful to route the wires correctly. Put the keyboard in place and push in the keyboard ribbon connectors. Make sure there are no tools or bits of solder or wire loose in the computer, They could cause a short circuit. Replace the cover. Power up. You should get the normal startup sound and message. If you do not, then switch off immediately and check all your connections. If you had no sound, check the speaker connection very carefully. If you had any other problems, remove the project from your machine and contact me! If the power up was normal, test out the project by loading files into sideways RAM banks 6 and 7: *SRLOAD <filename> 8000 (6 to 7) Q Then flip the switch and repeat. In this way you will find out which switch position gives you 1*64K ROM bank in slots 6 and 7 with the ROM enabled and which switch position gives you 2*16K RAM banks in slots 6 and 7 with sideways RAM enabled. You can flip between ROM and RAM at will. You will find that the RAM images are still there even after changing from RAM to ROM and back again. As I mentioned earlier, this project was for link 19 only. If you want to do the same with link 18 the procedure is exactly the same. You will then be able to toggle slots 4 and 5 between ROM and RAM. I intend to submit more articles like this in the near future. I have one planned for the good old BBC B, a project to freeze the computer. Has anyone any ideas for a project that they would like me to attempt on my BBC or Master? Happy soldering....!                                    