The WindHover 288K SuperRam Modification For The Atari 800 PC By Jay Torres Copyright (c) 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986 All Rights Reserved NOTICE This modification is intended for use in the Public domain ONLY! ALL rights to this modification are RESERVED by myself as the ORIGINAL AUTHOR. Anyone is free to use this information or publish it in any publication PROVIDED crerdit is granted to both myself and The WindHover Project. DUE TO THEIR REPEATED FAILURES TO ACKNOWLEDGE THE ABOVE AND PASS OFF MY WORK AS THEIR OWN THIS PERMISSION IS EXPRESSLY FORBIDDEN TO DAVID G. BYRD AND S.N.A.C.C. OF NEVADA! When I first got my Atari 800 back in 1978 I ran into the limitation of memory real quick. It only had 16k and the first program I typed in used more than that. Needless to say I upgraded to 48K not long after. I remember looking through ads for 128K ramdisks and wished I could get one but the cost was way too high. I resigned myself to a 48K machine forever. As time went by and I became more familiar with the machines' architecture, I became aware that the engineers at Atari left a lot of openings for further development. One of these wss for extra memory. The basis for this modification came from an unknown individual who worked in (of all places) Bell Labs in 1979. He (she?) had written a tutorial on the use of bank selection in 6502 based computer systems. Combining the information from that memo and the documentation I already had I resolved that year to give it a shot. The result was a 96K Atari. Encouraged by this early success the next three years saw me working on RAM expansion projects some more until it has reached its present form which I now refer to as the WindHover 288K SuperRam Modification. To build this you will need the following: a 74LSC02 quad NOR Gate, a 74LS175 Quad Latch, two 74LS158 Quad Multiplexers, a 74LS86 Quad XOR gate, a 74LS112 Dual Flip Flop and six 41256 Dynamic RAM chips rated at 200ns or better (I recommend Toshibas), some perf board, low profile sockets, and wire. MODIFICATION OF THE RAM BOARD 1. Take out a 16K RAM board from the 800 and remove the board from its casing. Looking at the board notice the eight chips along the top. These are the 16K RAM chips. The other four are addressing chips. 2. You will be removing the 12v and -5v sources on the board and then move the 5v source to the old 12v position. Cut the trace from Pin X of the RAM connector edqe to the capacitor located at C521. Also cut the trace going from edge Pin Y to C523. Be sure you cut these traces completely. Refer to Figure 1. 3. Using a soldering iron remove capacitors C521 and C523. 4. Pin W of the RAM edge-connector carries 5v. Using a short piece of wire make a bridge connection between this pin and the old 12v trace at the point where C523 was. 5. Remove the following capacitors along the top of the RAM board: C503, C505 C507, C509, C511, C513, C515, and C517. 6. Remove the eight 16K chips from the RAM board and insert the 256K chips in their place. Be careful, these chips are very sensitive to static electricity. 7. Using an ohmmeter check and make sure there are no connections between Ram board edge Pin Y and Pin 8 of the RAM chips. There should also be no connection between any two of the RAM edge pins (W, X, and Y). Since the addressing circuit has not been changed yet the board should still work like a 16K board. Place the board into the 800 and check to see that it works like a normal 16K board. If not recheck your work. 8. Remove the RAM board from the 800 and remove the 256K chips. Place them aside, in an antistatic tube or on an antistatic pad. 9. Cut the wide trace on the IC side of the board. This will remove the 5v source from Pin 9 of the RAM chips. Refer to Figure 2. 10. Picking up one of the new 74LS158 chips carefully bend up all of the pins with the exception of pins 1, 8, 15, and 16. 11. Remove the 74LS158 chip from Z503 on the RAM board. 12. Place the new 158 chip on top of the 158 chip from the board and solder them together: Pin 1 to Pin 1, Pin 8 to Pin 8, Pin 15 to Pin 15, and Pin 16 to Pin 16. 13. Insert the piggyback pair into Z503 of the RAM board. 14. Pick up the other 74LS158 chip and carefully bend up all of the pins except pins 8, l5, and 16. 15. Remove the 74LS158 chip from position Z504 of the RAM board and solder the new 158 chip an top of it in the same manner as the Z503 pair: Pin 8 to Pin 8, Pin 15 to Pin 15, and Pin 16 to Pin 16. This finishes the initial preparation of the RAM board. Now you must install the four new chips used to address the new superbanks of memory. While you can use glue to attach the chips directly to the RAM board, I recommend using a small piece of perf board and low profile sockets for the installation. I used double sided tape to attach the assembly to the board. That way you can replace the chips in the future in case one goes bad. Either way, place a small piece of tape to remind you of the chip type and the position of Pin 1. 16. Referring to Figure 3, wire the new addressing module. Connect Pin 1 of the module to the 5V power line located an the chip side of the board at the old location of C523. Use the left hand most pad. A good location for the ground line is the right hand pad where C513 used to be. Use short wires for all your connections. This will cut down on RFI emissions. 17. Connect a jumper from Pin V to Pin W of the RAM board. Put the board back into the 800 and apply power. 18. If the blue screen does not come up right away, shut the power off and recheck the connections. If it comes up alright then remove the board and take off the jumper you placed between Pin V and Pin W. 19. Cut the traces between RAM edge Pins M and N, P and R, and S and T. Put the board aside. 20. Remove the other two 16K RAM boards from the 800. Take them out of their cases and cut the traces connecting RAM edge Pins M to N, P to R, and S to T on each board. Put them back in their cases and put them aside. Now you must make a small modification to the ROM board in order to access the extra RAM at the D7xx window. 21. Remove the ROM board from the 800 and take it out of its case. Connect a jumper wire from Ram edge Pin 20 to Pin 7 of the 74LS138 chip located at Z401. 23. Put the ROM board back in its case and put it aside. The final portion of the modification involves rewiring of the 800 mother board. 24. Remove all cables from the 800 and flip it over allowing the joystick ports to face towards you. 25. Remove the five screws with a phillips screwdriver. Lift the bottom of the 800 off and put it aside. 26. Remove the screws holding the 80O circuit boards to the top of the case. 27. Pull the motherboard assembly up at the front and disconnect the keyboard ribbon wire from its socket. Disconnect the speaker and the RF cable also. 28. Now lift the motherboard assembly out of the casing. Put the casing aside. 29. Turning the assembly over so the RFI casing is on top, separate the power module from the main unit and put it aside. 30. Turn the motherboard over and take off the screws on the bottom. Turn the motherbcard over and lift off the RFI case. 31. Take the CPU card out and put it aside. To remove the bottom shield use a pointed screwdriver to push the center of the plastic cotter pins located at each corner out. You can throw these away since you really don't need them. 32. Turn the motherboard over and look at the backplane. Use Figure 4 to install all seven jumper wires. At this point all that remains is to reassemble the computer. Put the CPU board back in the mother board and place the unit into the RFI case. Put the bottom shield on the unit and replace the screws. Next, reconnect the power module and the RF cable. Place the unit into the top of the casing and reconnect the keyboard and speaker. Screw the unit back into place and finally replace the bottom of the 800. Now the big test. Put the ROM Card back in the front slot. Place the RAM cards back into the 800, making sure the 256K card is in the center slot. Power up the computer. If the blue screen does not come up, turn it off and check your connections as before. If the blue screen does come up then you are allowed a moment of insanity. You now have a 288K RAM system. Using the OMNIMON! RAMDISK Handlers If you have an OMNIMON! chip from CDY Consulting and would now like to use its resident RAMDISK handler there are two ways to do it. Method Number 1: This involves the actual reprogramming of the OMNIMON! chip itself. OMNIMON! uses CFFF hex refer to its RAMDISK handler. You will need to follow the instructions included with OMNIMON! to download it to disk. Find all references to CFFF and change them to D7FF. Using an EPROM program write the modified OMNIMON! code to a new EPROM and install it into the ROM card. This will not affect any of the other OMNIMON! functions and will allow access of software which use LEGAL calls to the OS. Method Number 2: This involves the addition of a DPST switch. Connect the center pole of the switch to Pin 7 of the 74LS138 chip of the ROM card. Connect one of the outer poles to Pin V of the ROM card. Connect the other pole to Pad H of the OMNIMON! board. Place the switch wherever it is most convenient for you. You will find in one position the SuperRam modification works normally. In the other position it will access the OMNIMON! Ramdisk Handler with one limitation; software which occupies memory at or above 40OO hex will cause conflicts. Software such as the Happy Enhancements' sector copy utility, will recognize the SuperRam modification upon bootup under these methods. SuperRam RamDisk Capabilities The use of the OMNIMON! Ramdisk handler will allow uou to boot from the SuperRam modification using any DOS developed for the Atari PC. This way you can have a 720 sector, single density RamDisk. If you want to use a 720 sector, double density Ramdisk drive just send me a disk in a SASE or $10.00 to help cover my costs and I will send you a DOS which is fully compatible with Atari 2.0 and 2.5. This includes the RamDisk, initializer, R: handler for the 850 interface and an additional 720 Sector Single Density RamDisk DOS too. All in all, the Atari 800 has always been, in my humble opinion, the flagship of the 8-bit Atari line. With its open architecture and available documentation there is still no system I can think of that allows the home computer-enthusiast to do as much. After almost seven years my 800 is still going strong. Sure, a new 130XE with 32OK of RAM sits next to it now, but even so, I think the XE knows who's the head CPU.