ѓ VDC Upgrade Info X% PRG formatted GEOS file V1.0 ї ?я 'яа$ $яь$Ђ$Ђ$µ4$Ґ$$µ4$Ґ$$Ґґ$Ђ$‚$‚<Џ„‚‚ Ђ яьѓ яя Write Image V2.1 Red Storm geoWrite V1.1 р This file was created with Wrong is Write. Written by Joe Buckley. °Н я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я я @ ђ а 0 UPGRADE YOUR VDC RAM TO 64K By: John Kress Copyright 1986 Twin Cities 128 P.O. BOX 4625, Saint Paul MN 55104 $2.50 per single issue $25.00 for a 12 issue subscription This article has been released for non-profit use only, provided the author's name and the above information are presented with the article: The very first time I had fired up my new C-128 I loved the 80 column screen. I remembered the days of my Vic-20 with 23 characters per line. Now I had a computer with an 80 column screen and I thought to myself 'Now I own a real computer'. Then I came across a very basic 80 column graphic program that used a joystick, and thought that this is great, but it is too bad that you can only use one color on the screen at a time, and secretly dreamed of owning an Amiga. Then came the day that I found out that the memory dedicated to the Video Display Chip could be expanded from the stock 16K to 64K of RAM. Right then and there I was hooked (I believe it's referred to as 'Technolust' in these parts) and wanted to learn all I could about expanding the RAM to its maximum. I should explain a bit about the VDC and it's RAM. The 80 column screen uses a separate chip for screen processing, and that chip has its own dedicated RAM. Unlike the VIC chip, for the 40 column screen, which uses part of the BASIC RAM for screen memory, the VDC has 16K of RAM tied into it that cannot be accessed in the normal peek and poke method. The VDC is in some ways a separate processor that operates independently from the rest of the C-128, and is able to work at a faster clock speed than the VIC chip. That is the reason why the video display goes blank on the 40 column screen when the FAST command is issued. Why expand the VDC memory? Since my major computer interest is GRAPHICS, I wanted to find out how things might be improved with more memory. One of the first things I pondered was the graphics screen with attribute RAM for color. That would allow more than one color on the screen; although you're still limited to just one color in any 8*8 pixel area, you can have more that one color. Then there is the ability to have a combination of screens in VDC memory, up to 4 graphic screens, up to 13 text screens, or a combination of both. There is also the possibility of making up different fonts (print styles) in memory and being able to change them. (Editor's note: The execution of this process will void your computer's warranty. Readers who attempt this process do so at their own risk. Neither this author or Twin Cities 128 will take responsibility for losses due to the attempted execution of the process outlined in this article.) The parts you will need are : * Two (2) 18 pin IC sockets, to be used to hold the RAM chips. These can be found at most any electronic supply house. * Two (2) 4464 Dynamic RAM Chips, with a speed of 120 ns. Yes that's correct, 4464 RAM chips, I know that the Commodore Programmers Reference Guide says 4164 RAM chips, but 4164 chips are a sixteen pin type. The 4416 chips are an 18 pin type so if you try to use the 4164's you'll have two extra holes and nothing will work right. You will need the following tools: Wire cutter or nippers. A small pencil type soldering iron (35 watts is be enough, much more may get too hot.) Some rosin core solder or better yet, Solid core solder and a paste type non-corrosive flux. Small phillips screwdriver. Small pair of pliers. Now you're ready to begin: @ ђ а 0 NOTICE: Integrated Circuits are extremely sensitive devices, and very sensitive to static charges. A small static shock to a IC is as deadly to them as a bolt of lightning would be to a human. Take extreme caution to avoid a static discharge to the computer. First thing to do is remove all power cords and serial connectors from the C-128. This means everything, since the main board must be removed from the machine. @ ђ а 0 Turn the computer over and locate and remove the six (6) screws holding the computer case halves together, then carefully separate the halves. This is critical, because the keyboard and power light connector along with a ground braid for the keyboard are still connected and could be damaged. Carefully remove the screw holding the ground braid, along with the connectors for the power light and keyboard, taking note of their proper connection. I found that the keyboard connector was installed with a brown wire closer to the power switch, but things may be different on other machines. The next step is to remove the screws holding down the computer board and the ground casing. There were six screws around the perimeter of the main board/shield assembly, remove all of these. Then you must use the pliers to gently bend the tabs holding the upper ground casing to the lower casing. There is one more screw mounted on the ground casing in about the top middle, this must be removed also. There is one spot where the casing halves were soldered together on my computer and that was in the front right side, near where the numeric keypad sits. Carefully unsolder the halves and lift the top half away. What you now see is the main board with a small metal box on it, near the center of the board. The chips that need to be replaced are inside that metal box. Inside the box are both of the screen controllers, the 8564 Vic chip and the 8563 VDC chip. Remove the lid to the box and locate the two chips that are identified on the circuit board with the marking U23 and U25. On my board these chips were labeled with a large F and the part number MB81416-12. The number may vary due to the manufacturer, but the markings on the board will identify the correct chips. Now for some very delicate surgery. Since the RAM chips will be discarded, I suggest that you carefully cut away the chip pins (leads) from the body of the chip. This will make removing the remaining portion a lot easier, and leaves less of a chance of damaging the main board than trying to remove the whole chip, intact. The next step is to carefully unsolder the pins from the circuit board. Make sure that you are working with the correct area, as things do get rather confusing when you turn the board over and notice all of the many soldered areas. You might be best off to mark the correct area with a felt tip pen to avoid confusion. The next step will be to install the IC sockets into the circuit board. Try fitting the sockets into the board to make sure that they will fit all of the way through the holes and that there is enough material poking through for a good solder joint. Also be sure to orient the sockets with the small identification notch on the correct end of the board. The notch is printed on the board so you should have no trouble. When you have the sockets installed correctly, lightly bend the pins over to hold them in place and you're ready to solder them in place. Again be careful, as drips of solder can cause a short, and a cold solder joint will cause a poor connection. Now you're ready to install the 64K chips in the sockets, carefully inspecting the pins for proper alignment. Most of the time chips will be made so that you will have to bend the pins inward, toward the center, to fit properly in the socket. But too much bending will break off a pin. Once you've installed the chips you're ready to start the reassembly process, just reverse the disassembly steps and make sure to solder the ground case halves again. Reconnect your cables and power up the computer. If all went well, you should see NOTHING UNUSUAL. The same old cold start up message and nothing different. Some of you might notice a different pattern on the screen when the initialization process is going on but after that you should see the same OLD SCREEN. The cold start routines for the C-128 initialize the VDC registers, and the VDC chip is told that it still has the 16K chips in it. In order to tell the VDC you've upgraded the RAM, you will have to set bit 4 of register 28. When this is done, for some reason, the character information gets scrambled, but a call to the COPY ROM routine at $CE0C clears the problem. If your screen does not appear the way is should, look for a cold solder joint or a pin that is not installed into the socket correctly. I found that when I tried to remove the old chips in one piece, I had damaged a portion of the copper foil on the circuit board and had to trace the circuits out and install a jumper wire from the 8563 socket to one of the RAM sockets. (New Horizon Software Notes) To check your upgrade, run one of the Landmarks Series applications that uses the expanded video RAM.