IMPORTANT: You can now order custom cartridges from Atari Age. Of course, this page is still useful for anyone who is learning electronics or just likes to tinker.

 
The F8 bankswitch convention works the following way:
     
Address      1 1111 1111 1000  Go to bank 0
             1 1111 1111 1001  Go to bank 1
             ----------------
PinName      A AAAA AAAA AAAA
             1 1198 7654 3210
             2 10     

One way to do this is to put a detection circuit on
A1-A12 which clocks A0 into a flip-flop as the bank
value.  There may be easier/cleaner ways to do this
but I think three chips (7404,7474,74133) with a 
deglitching cap isn't that bad.



                       |\      
          -------------| >()--------------  Eprom
         |             |/                   Enable
         |                       5v  5v
    A12 -+-|-                   __|___|_
    A11 ---|  \                | Set Rst|
    A10 ---|   \               |        |
     A9 ---| 7  \          A0--|D  7   Q|-- A12
     A8 ---| 4 N \             |   4    | of eprom
     A7 ---| 1 A |     |\      |   7    |
     A6 ---| 3 N |()-+-| >()---|>  4    |
     A5 ---| 3 D |   | |/      |________|
     A4 ---|     /   |           
     A3 ---|    /   ___         
    /A2 ---|   /    ___ 1000pf (0.001 uf)
    /A1 ---|  /      |
        \--|_/       |
                    gnd


Eprom must be tied to 2600 D0-D7 and A0-A11 directly 

/A1, /A2, A12, Nand output inversions done with 7404 chip

/A1 goes to two pins on the NAND gate because it has 13
inputs.  You can use some other signal though 

The 2600 A12(cart enable) and eprom A12 are completely
separate animals

The 7474 is a dual D flip-flop, you can use something
equivalent

Stargate (Defender II) is the only F8 game that uses the
Atari Ram.  It won't work without it. 

If you're making a multicart, put two 4k games at
the front or end of the eprom.  Do NOT put one or three
or an odd number, you'll screw up the 8k address 
boundaries.  Check that a 4k game works, then try F8
games so you're not trying to troubleshoot everything at
once.

If it works with 4k games but not F8, and you are sure
it's wired correctly, you may need to play with that
cap value, it might be sensitive to the IC logic family
and speed. You can also try putting three inverters in
a row and put a cap in the middle, maybe even with a serial
resistor. 

Here are the part pinouts:

      +---+--+---+               _____________
    A |1  +--+ 16| VCC      /Y = ABCDEFGHIJKLM
    B |2       15| M
    C |3       14| L
    D |4   74  13| K
    E |5  133  12| J        13-input NAND gate.
    F |6       11| I
    G |7       10| H
  GND |8        9| /Y
      +----------+


        7474   Dual D flip-flop with set and reset.

      +---+--+---+           +---+---+----+----*---+---+
/1RST |1  +--+ 14| VCC       | D |CLK|/SET|/RST| Q |/Q |
   1D |2       13| /2RST     +===+===+====+====*===+===+
 1CLK |3       12| 2D        | X | X |  0 |  0 | 1 | 1 |
/1SET |4  7474 11| 2CLK      | X | X |  0 |  1 | 1 | 0 |
   1Q |5       10| /2SET     | X | X |  1 |  0 | 0 | 1 |
  /1Q |6        9| 2Q        | 0 | / |  1 |  1 | 0 | 1 |
  GND |7        8| /2Q       | 1 | / |  1 |  1 | 1 | 1 |
      +----------+           | X |!/ |  1 |  1 | - | - |
                             +---+---+----+----*---+---+



      +---+--+---+             +---*---+          _
   1A |1  +--+ 14| VCC         | A |/Y |     /Y = A
  /1Y |2       13| 6A          +===*===+
   2A |3       12| /6Y         | 0 | 1 |
  /2Y |4  7404 11| 5A          | 1 | 0 |
   3A |5       10| /5Y         +---*---+
  /3Y |6        9| 4A
  GND |7        8| /4Y       Hex inverters.
      +----------+