The WindHover Atari 400 SuperRam Modification by Jay Torres and Jerry Rombert The WindHover Project (Formerly SAMSON A.C.E.) Copyright (c) 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986 All Rights Reserved NOTICE: This information is placed into the Public Domain for the use of all users of the Atari (6502)PC. It may be reprinted by anyone provided credit is given to the authors and The WindHover Project. Due to their failure to have done so in 1979 and causing our work to be referred to as the MACE Mod this permission is expressly DENIED to M.A.C.E. Let's face it. The Atari 400 PC in its original configuration is good for slapping in cartridges and playing games but little else. If you want to use a good sized program you were out of luck unless you bought a memory expander. Prices on these ranged from $95 to $170 depending on what you wanted. Problems arose with software compatibility which would check for a max of 48K. If there was more than 48K the software would not boot. Not too great. This article addresses the question of expanding the memory of the Atari 400 to include a maximum of 64K RAM. The manner in which it will be done will allow all software to boot in without complications. Best of all, it will cost less than $25.00. You will need the foillowing parts: 8 4164 200ns(or faster) Dram chips, 1 74LS158 quad 2-1 multiplexer, 1 74LS02 quad NOR gate, 1 74LS74 dual flip flop, 1 74LS00 quad NAND gate, 2 680 ohm 1/4W resistors, plus wire and fine soldering equipment. 1. The first step is to open up the 400 and remove the motherboard. To do this turn the 400 over and remove the bottom screws. 2. Turn the 400 over, open the cartridge door and lift the top panel up and over. 3. Remove the keyboard by pulling straight up on the connector. 4. The circuit board to the right is the power supply board. Remove the two screws that fasten its left side to the right side of the metal case. Gently but firmly pull the left side of the power supply board up until it is free. Be sure to remove the plastic interlock from the cartridge slot area before you do this. 5. Now remove the speaker connector and lift the metal case out. 6. Turn the metal case over and remove all of the screws in the metal plate. 7. Pull the main board up and out of the metal case. 8. Place the motherboard on a non-static surface with the joystick ports towards you. 9. The first board sticking up is the RAM board. Remove it, the CPU board behind it, and the beige cartridge slot piece from the motherboard. Place the motherboard aside for now. 10. Look at the RAM board. The eight chips along the top are the RAM chips. The other four are addressing chips. 11. You shall be removing the 12V and -5V sources on the board and moving the 5V source to where the 12V used to be. 12. As shown in Figure 1, cut the trace from Pin X of the card edge connector to C521. 13. Cut the trace going from edge pin Y to C523. 14. Remove C521 and C523. 15. The trace coming from pin W carries 5V. Using a short piece of wire make a solder bridge between this trace and the old 12V trace at the point where C523 used to be. 16. Remove C503, C505, C507, C509, C511, C513, C515, and C517. 17. Remove the eight 16K DRAM chips and insert the 64K DRAMs in their place.(NOTE PIN 1!) 18. Using an ohm meter, insure there is no connection between edge pin Y and pin 8 of the DRAMs. There should also be no continuity between any two of the edge pins W, X, and Y. Assuming all has gone well the board should function exactly as a 16K board since we have not yet changed the addressing circuitry. Now is a good time to check the board. If you wish, reassemble the computer and check to see if it works as described. If it doesn't work recheck all connections and disconnections. 19. Now remove the 5V supply from Pin 9 of the DRAMs. To do this cut the wide trace on the chip side of the board as shown in Figure 3. 20. Pick up the 74LS158 chip and carefully bend up all of the pins EXCEPT pins 1, 8, 15, and 16. 2l. Remove the chip at Z503 from its socket and place the 74LSIL@-8 on top so that the four pins listed above touch the same four pins on the lower chip. Carefully solder the four pairs together. 22. Solder a four inch piece of wire to each of pins 2, 3, and 4 of the top chip. 23. Reinsert the chip pair at Z503. 24. Solder the wire from pin 2 into the hole attached to edge pin M and the wire from pin 3 to edge pin U. 25. Solder the wire from pin 4 to a hole in the former 5V bus (the wide trace along the top of the chip side of the board). The memory board is now complete and shall function as a 48K RAM board. With an ohmmeter check each of the connections diagrammed in Figure 3. The next stage involves a modification of the motherboard itself. Figure 4 is a partial schematic of the needed connections. 26. Locate Z103 forward of the memory slot. 27. On the underside of the board cut the traces leading from pins 1 and 2 of Z103. 28. Attach a wire from pin 24 (across from pin BB) on the underside of the CPU board slot to pin U under the memory slot. 29. Attach a second wire from pin CC under the CPU slot to Pin M under the memory slot. 30. Now wire the circuit of Figure 4. 31. On the 14 pin socket solder pins 3 and 4 together with a short piece of bare wire. Do the same to pins 2 and 13. 32. Solder an 8 inch piece of wire to each of the pins 1, 5, 6, 7, 11, 12, and 14. 33. With these wires make the six connections to the underside of the cartridge slot as diagrammed. 34. The seventh wire from pin 1 goes to Pin 18 on the underside of the memory slot. 35. Plug the 74LS02 into the socket and bend the wires around the edge of the motherboard. It is a good idea to place the chip on the motherboard in the dead bug position with double-sided tape. 36. Finally solder one of the 680 ohm resistors between pin A under the cartridge slot and the nearest ground connection. Be very careful that you do not create solder bridges. 37. Put the second 680 ohm resistor between ground and pin 14 under the cartridge slot. The 48K RAM modification is finished. Recheck ALL connections. Reassemble the computer. Plug in the 400 and turn it on. If the blue screen doesn't come up quickly, TURN IT OFF IMMEDIATELY and recheck your work. If you exercised proper care you should now have a 48K Atari 400. Figure 5 shows a circuit which will allow you to access the extra 16K on your modified board. After you have successfully completed the 48K modification as described above disconnect the wire you placed between edge pin U and pin 3 of the 74LS158. Wire the circuit of Figure 5 in its place. Two chips are required for this circuit: a 74LSOO Quad NAND Gate and a 74LS74 Dual Flip-Flop. They may be wired to the memory board in sockets as you did with the 74LS02. The NOR gate on the left is from the 74LS02 chip you wired to the motherboard. Bring its output to the memory board through an unused edge pin such as V. The additional 16K is banked switched with the middle 16K of the 48K RAM. Although you need to be careful in using it can come in very handy for storing additional graphics or using it as virtual memory. This is best done in machine language since Basic is both too slow and could erase needed code. The Windhover Project has developed a DOS which will access the extra RAM and make it work as a virtual mini-disk. It is 100% compatible with Atari DOS 2.O and allows both an instantaneous call to the DUP.SYS and generates a MEM.SAV file to save data you were working on in memory. (DOS 2.5 will also use this as a 100 sector ram disk-RLD). To get a copy of the DOS just send a SASE with a disk or $10.00 (money order only please) to help cover my costs. Money order should be made out to Jay Torres. end.