building the MEGA4000
=====================

1. parts list

U1  = GAL20V8 programmed (Adrdec 1 or Shar'dGAL)
U2  = GAL16V8 programmed (Adrdec 2 or Shar'dGAL)
C1  = 100nF Keramik capacitor (only adaptor for the Color Master)
C2  = 100nF ceramic capacitor (only adaptor for the Color Master)
R1  = 330Ohm
ST1 = DIN41612/AB/Wirewrap female (MEGA bus)
ST2 = ISA Slot (angled)
ST3 = AMD plug for power supply
      socket 24 pins (small) (for the GAL20V8) (*)
      socket 20 pins         (for the GAL16V8) (*)
      some wire for the power supply

(*) When building the adaptor for the Cardek board you should use 
    sockets with integrated capacitors. When making your own PCBs it's 
    better to use SIL precision contacts since you have to solder them 
    from both sides.
    
2. Prices

GAL set programmed: 30DM + package/mailing

PCB:                          11,00DM
ISA slot:                      6,00DM
Power supply plug with cable:  3,70DM

PCBs are only available for the Color Master version (since the wrong 
layout went into production (it's not my fault) four GND connections 
for the highest address lines on the ISA extension slot (A20-A23) are 
missing and have to be wired manually. When there are enough requests 
the Cardek version will also be produced.

Important: If you do just some requests please do by EMail.

How to order: I will not handle orders from outside Germany normally. 
              But there are some people putting this product in their 
              shareware distribution shemes. So watch out...

3. building it...

All parts except the ISA slot are placed on the soldering side of the 
PCB! In case of the Cardek adaptor you will need a bridge (some piece 
of insulated wire) on the components side. Just take a look at the 
parts placement image. For the Color Master version you should solder 
the MEGA bus connector first. In case of do-it-yourself PCBs you 
should solder all pins from both sides to achieve higher stability.
You should solder the MEGA bus connector with an angle of around 10 
so that the card is nearer to the mainboard at the back of your 
computer than at the front. It is necessary to have as much space as 
possible at the front side if you want to use the PAK/3 + FRAK. A 
PAK/3 + FRAK + buffer PCB won't fit together with the MEGA4000!
In this case you need another case for your computer. In case of the 
Cardek TC version it's quite difficult to solder the sockets (use only 
precision types!) from both sides. It's up to you to find out the best 
way...
When using SIL contacts you should check for short circuits after 
every row of contacts you soldered. It's nearly impossible to correct 
mistakes afterwards. At least you should solder the ISA slot. You 
should also solder as many pins as possible from both sides for 
stability reasons.
So you will need a soldering iron with a very fine tip.
At last you need to solder the power supply wires. The 12V pin is that 
one where only a single line leaves. The three GND pins are in the 
"middle" of the connector, the two 5V pins are at the opposite side 
from the 12V pin. Check twice! A mistake will cause serious damage to 
your hardware!

Modifications for some graphics boards:

The Color Master has a 100nF capacitor applied to the reset line 
(C27). That's nonsense! Software resets won't work. So just remove 
that capacitor.

You may want to exchange the 14,318MHz Oscillator by a 16MHz or 18MHz 
type to get higher resolutions. With some boards you can use up to 
95MHz dot clock together with NVDI.
Warning! The ET4000 chip, the RAMDAC and the memory chips will heat up 
much more than normal after such a modification! So be careful! Do it 
at your own risk!

4. Test

First you should test the adaptor without GALs and graphics board. The 
computer must behave like before. If not you may have some short 
circuit on the board. When it works insert the GALs. The computer 
should still behave normal now. When you have a debugger (e.g. TEMPLMON)
you may check if you can read and write to the memory and IO locations 
of the board.
Now it's time to insert the graphics board. For a first test you don't 
need the -12V even when the graphics board requires it. Don't connect 
a monitor to the card at this time!
You can initialize the board "by hand" using a debugger. The following 
commands are for TEMPLMON:

:FF03C3 01   ; Video Subsystem Enable, Address $03B0
:FF03BF 03   ; Herkules Comp. Register, Set KEY
:FF03D8 A0   ; Display Mode Control, Set KEY
:FF03D4 36   ; CRTC Index -> Select CRTC Reg. $36
:FF03D5 F1   ; Video System Configuration 1, 16Bit I/O, 16Bit MEM,
             ; Memory contiguous

Don't type in the comments beginning with ; ...

When writing to $FF03D4 you should be able to write values from 
$00-$3F. When using higher values the upper two bits are ignored and 
always read as zeros.

:FF03D4 15   ; CRTC Index -> Select CRTC Reg. 15
:FF03D5 xx   ; Vertical Blank Start Bit 0-7
Doing write/read accesses at $FF03D5 you should be able now to write 
and read all values from $00-$FF.

What to do when it doesn't work?

One problem is the MEGA bus connector itself. These are hardly 
available with double sided contacts. But at the single sided version 
the contacts 1, 2, 63 and 64 get jammed quite often. So press the 
halves of the plastic case a little apart and put a short piece of 
wire in between. The connector should work reliable now. 

When all is working up to now it's time to load the VMG. The first 
action shall be the measurement of the pixel clocks. The sound option 
should be activated in your control panel because the VMG gives a 
series of beeps when doing the measurement. You should then save these 
options and load and try out the SVGA.INF file. When something strange 
is going on turn your VGA monitor off immediately!!!

Even with a quite simple project such as this there are a lot of 
possibilities for errors and failures. I can't help at this point so 
the best way is to find someone who knows the Atari hardware good 
enough and let him/her help you.

When it works?

Well, in this case have fun with your MEGA4000!

5. Other Atari Computers

I received requests about the other Atari systems like MEGA STe or TT.

- MEGA STe/TT
  I would have to develop a VME card. The ET4000 board must be 
  connected "somehow" to this. The problem: Do you want a shoebox 
  behind your computer? What about wiring?
  Who is giving me a MEGA STe for the development?
- 1040ST/520ST/260ST
  Here it's quite simple: You need an adaptor connecting the 68000 bus 
  to a DIN41612 plug 1:1 except for the VCC pins. There is an example 
  included in the archive.
  But the "small" systems are not so stable like the MEGA STs so you 
  may experience DMA problems etc.
- 1040STe
  You need an adaptor for the PLCC CPU used in the STe. These parts 
  are not easy to get - I have no source for these parts, sorry.
