Upgrade Your VDC RAM to 64K (fwd)

[RobertB]

From:     Al Jackson
Date:     Sat, May 9, 2009 9:24 am


The BASIC 8 program on the Megabit ROM requires an expanded Video RAM. In addition, the Maverick Copy programs will make use of the expanded RAM if present. The Maverick "64K VDC RAM Test" on the ROM will check your C128 for presence of the Expanded Video RAM.

The 128DCR came with the Expanded RAM. The regular C128 did not.

The following is an article explaining the Video RAM & instructions so you can install your own:

      UPGRADE YOUR VDC RAM TO 64K
            By: John Kress

  Copyright 1986 Twin Cities 128
  P.O. BOX 4625, Saint Paul, MN 55104

  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 its 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: 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:

  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.

  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.

[waltermixxx]

Groovy article...

  I was all set to do this when I found this:

http://cgi.ebay.com/Commodore-128-64K-VDC-Video-Memory-Upgrade_W0QQitemZ310140166785QQcmdZViewItemQQptZUK_VintageComputing_RL?hash=item4835cb6281&_trksid=p4634.c0.m14.l1262&_trkparms=%7C301%3A1%7C293%3A1%7C294%3A30

it appears as though there are still some 64K solderless VDC upgrades still kicking around...
I purchased one about three weeks ago, and it arived last week... I installed it in about, 15 minutes,
it was very cool...looks like they have some more on ebay...

it was very exciting for about 15 minutes or so (my wife never really got it...),  now I pretty much internalize my excitement when I turn my 128 on just knowing there is 64K of video ram instead of the usual 16K waiting to be utilized some time soon...

then I went and bought an SD2IEC from NKC Electronics...( somebody stop me already...) it should be here soon...

http://www.nkcelectronics.com/sd2iec-boar2.html along with one of those handy dandy EX1541/MX1541 interface thingies...

http://www.nkcelectronics.com/commodore-xexm1541-ada1541.html

hours of fun...

I can't remember why I brought all of this up?

oh yeah now I remember, the 64K VDC upgrade for your Commodore 128,  nice and easy with the piggy back board.

cheers. My 15 X 2764 and my 15 X 27128 eproms arrived as well..now I just have to make something....

actually now I just have to get the ethernet card Jbrain is working on, once they are ready, I would like to get one of those too...
perhaps I will create a webserver with my 128, with custom software on ROM, and the sd2iec as storage?

[RobertB]

it appears as though there are still some 64K solderless VDC upgrades still kicking around...
I purchased one about three weeks ago, and it arived last week... I installed it in about, 15 minutes,
it was very cool...looks like they have some more on ebay...

Yes, this solderless VDC upgrade board is still available.  FWIW, long ago in one of the C= magazines, it was pointed out that the solderless VDC upgrade was slightly incompatible, but in my experience I've never had a problem with it.

then I went and bought an SD2IEC from NKC Electronics...( somebody stop me already...)

Addictive, isn't it? 

                Truly,
                Robert Bernardo
                Fresno Commodore User Group
                http://videocam.net.au/fcug
                July 25-26 Commodore Vegas Expo - http://www.portcommodore.com/commvex

[BigDumbDinosaur]

The following is an article explaining the Video RAM & instructions so you can install your own:

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.

The VDC's speed has nothing to do with why the 40 column display goes blank when the FAST command is issued.  The reason that happens is because the BASIC code that processes the FAST command doubles the clock rate and then tells the VIC to discontinue display updates.  Without the latter, the VIC would display garbage, as it won't have enough time to get to the memory bus.  BTW, disabling VIC display updates slightly accelerates the machine, even in one MHz mode.

* Two (2) 18 pin IC sockets, to be used to hold the RAM chips. These can be found at most any electronic supply house.

It's best to use sockets with gold plated machine-tooled pins.  The tin plate stuff can be flaky.  However, avoid using sockets if you can.

* 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.

DRAM faster than 120 ns is okay, as is CMOS DRAM.  You won't see any improvement in performance, though.

A small pencil type soldering iron (35 watts is be enough, much more may get too hot.)

The C-128's mainboard is not very tolerant of heat, so be sure to work fast to avoid having traces and pads lift from the board.  Adding to the problem is the age of the stuff, which means the bond between the copper and fiberglass will have deteriorated.

Some rosin core solder or better yet, solid core solder and a paste type non-corrosive flux.

NO!  NO!  NO!!!  With rare exceptions (mostly SMT work), never use paste fluxes of any type for electronic soldering.  Use only rosin-core lead/tin solder, ideally 63/37 alloy.  DO NOT use RHOS-compliant solders of any kind on old PCBs, as the heat required to work with them will cause pads and traces to lift.  Be sure to clean flux residue after you're done.

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.

If you are using the 80 Column Display Manager on a machine with the 1985 ROMs, it will automatically detect the amount of installed VRAM and if it is 64K, will configure the VDC to recognize it.

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.

The scrambled information occurs because setting bit 4 in register 28 changes the way the VDC addresses the RAM, invalidating the fonts copied from the character generator ROM.  Again, the 80 Column Display Manager will compensate and fix the font information for you.