2600 F6 Bank Switching


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IMPORTANT: You can now order F6 eprom boards made by Atari Age. Of course, this page is still useful for anyone learning electronics or who wants to make a 16k cartridge using the Atari Ram chip or make a multicart with both F6 and F8 bankswitching.

 
The F6 bankswitch convention is simply an expansion of the
F8 method and if you understand that one, you can get this.

It works the following way:
     
Address      1 1111 1111 0110  Go to bank 0
             1 1111 1111 0111  Go to bank 1
             1 1111 1111 1000  Go to bank 2
             1 1111 1111 1001  Go to bank 3
             ----------------
PinName      A AAAA AAAA AAAA
             1 1198 7654 3210
             2 10     

Parts List:
74133 13-input Nand gate (x2)
7404  hex inverter
7474  dual D flip-flop 
silicon diodes (x2)
12 kohm resistor (other values would probably work)
1000 pf (0.001 uf) capacitor (other values might work)


                       |\                   Eprom
         ,-------------| >()--------------  Enable
         |             |/                  
         |                               5v  5v
    A12 -+-|-            5v             __|___|_ 
    A11 ---|  \          |             | Set Rst|
    A10 ---|   \         /         A0--|D1    Q1|-- A12 of eprom
     A9 ---| 7  \    12k \         A3--|D2    Q2|-- A13 of eprom
     A8 ---| 4 N \       /             |        | 
     A7 ---| 1 A |       |    |\       |      7 |
     A6 ---| 3 N |()--|<-+--+-| >()-+--|>ck1  4 |
     A5 ---| 3 D |       |  | |/    |  |      7 |
     A4 ---|     /       |  |       +--|>ck2  4 |
     A3 ---|    /       ___ |          |________|
    /A2 ---|   / 1000pf ___ |
    /A1 ---|  /          |  |
     A4 ---|_/           |  |
                        gnd |
                            |
    A12 ---|-               |
    A11 ---|  \             |
    A10 ---|   \            |
     A9 ---| 7  \           |
     A8 ---| 4 N \          |
     A7 ---| 1 A |          |
     A6 ---| 3 N |()--|<----'
     A5 ---| 3 D |
     A4 ---|     /
    /A3 ---|    /
     A2 ---|   /
     A1 ---|  /
     A4 ---|_/

Does this circuit looks a whole lot tougher than the F8 one? Well it's not, it still needs only one 7404 and one 7474 chip. As for needing two 74133s, do you notice that only four pins are different between the two? Bend those four up (A1,A2,A3, and output) on one chip and solder it on piggyback to the other. Viola, no extra board space needed compared to F8 (you might need to cut a hole in your cart cover though).

The two diodes and a pullup resistor make a wired AND while the 1000pf cap provides deglitching. Either Nand gate can go low to clock the flip-flop.

Activision made their ntsc Double Dragon carts do F6 with four standard chips, but it's a different schematic. I was going to get one and trace it through, but then got lazy :)

If you put in switches to disconnect the bottom 74133 NAND output and also open the eprom A13 connection, you then have F8 bankswitching. This is what I do on my multicart.

If you are installing this on an atari board that uses the Atari Ram chip, the A12 signal above should be changed to the Ram output signal (the ram chip only passes on the A12 for non-ram addresses). See Kevtris for pinout.

For people who really want to get advanced, put a pulldown resistor on the Ram input and have a switch to take the Ram path or bypass it. Then you can have a multicart that supports 4k, 8k, 8k with Ram (Stargate), 16k, and 16k with Ram. That was how I made my multicart:


F6 multicart

Even though this multicart can swap eproms and play 95% of the 2600 library, it's still full-on ugly without a label. You need a cart extender to use this with a console because the eprom protrudes, however it's usually plugged into the portable instead. Portables and multicarts go great together :)

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