Tigervision Bankswitching

[jsoper]

For Tsukasa:

Here's some text I got from Kevin Horton and Chad Schell plus an ascii diagram I did up. Not 100% sure of the inductor values or the caps to ground.

 

-3F: Tigervision was the only user of this intresting method. This works

in a similar fashion to the above method; however, there are only 4 2K

segments instead of 4 1K ones, and the ROM image is broken up into 4 2K

slices. As before, the last 2K always points to the last 2K of the image.

You select the desired bank by performing an STA $3F instruction. The

accumulator holds the desired bank number (0-3; only the lower two bits

are used). Any STA in the $00-$3F range will change banks. This appears to

interfere with the TIA addresses, which it does; however you just use

$40 to $7F instead! :-) $3F does not have a corresponding TIA register, so

writing here has no effect other than switching banks. Very clever;

especially since you can implement this with only one chip! (a 74LS173)

 

 

They are the simplest things inside. normal 8K ROM and a 74xx chip.

It's a quad transparent latch. (can't remember the part # now exactly).

 

D0, D1 run to the inputs on the D inputs on the latch, and the 2 outputs

run to the upper address lines on the ROM.

 

/OE runs to A11, and there are pullups on the outputs so that when A11

is high, the outputs tristate but are pulled up. This selects the last

bank of ROM into the second bank in the 6502 address space.

 

when A11 is low, the outputs of the latches are in effect so it selects

the desired bank. The clock line is connected to A12, and the two enables

are tied to A6 and A7.

 

To get a valid latch, A12 has to go from LOW to HI, while A6 and A7 are

low.

 

 

74173



4-bit 3-state D flip-flop with reset, dual clock enables and dual output

enables.



      5v      5v

       |       |

       |       |

       /       /

  5.1k   5.1k                  +---+--+---+

       /       /   gnd______/OE1 |1  +--+ 16| VCC________5v

                 A11______/OE2 |2       15| RST________gnd

       |  A11__|______________Q0 |3       14| D0_________d0

 A12___|______________________Q1 |4   74  13| D1_________d1

                              Q2 |5  173  12| D2_________gnd

                              Q3 |6       11| D3_________gnd

                   A12_______CLK |7       10| /CLKEN1________,

                   gnd_______GND |8        9| /CLKEN2___,    |

                                 +----------+           |    |

                                            _______     |    |

                           A7___///_____|       |____|    |

                                  750      |_______|    |    |

                                              10uh     ___   |

                                                       ___   |

                                                        |    |

                                                        |    |

                                                       gnd   |

                                            _______          |

                           A6___///_____|       |_________|

                                  750      |_______|    |

                                              10uh     ___

                                                       ___

                                                        |

                                                        |

                                                       gnd

[Tsukasa]

As soon as the last part of my eprom programmer (power converter chip) gets here (before the week is out), I'll test it out!

My goal is to have a multicart for every bankswitching format.

 

Sorry to bother you so much...

As soon as school lets out, I'll have a nearly infinite ammount of free time so I'll be able to help out a lot of people....

[Susuwatari]

10uh is 10 microHenry, a measurement of inductor value. From the look of the diagram, it would appear its used tro slightly delay the signal from A6 and A7 so the timing of the bankswitch wouldn't be screwed.

 

Measuring Henry's aren't easy as most multimeter don't have that ability.

 

As for capacitor, it's probably a common run of the mill 0.1 uF caps used to drain the inductor.

 

@Tsukasa:

Better get in line. I'm already planning an F8 based multiucart as soon as one of the Al gets around to shipping me some F8 boards I ordered last week. F4 based multicart isn't poractical because there's only like 1 game that actually uses it and I don't know of any homebrewns that uses those. F6 maybe as there are around 50 or so that uses this but you may need an 8Meg EPROM for this one

 

After the F8 multicarts, I'm going to try and deal with the oddball Parker Bros (E0) multicart (I want Ewok Adventure and Lord of the Rings!) or even the complicated M-Network which only 3 uses this bankswitch scheme plus 2K RAM for Burgertime, I have a spare Burgertime with standard chips and not black blobs!.

[jsoper]

I have a spare Burgertime with standard chips and not black blobs!.

Can you trace that schematic out and post it?

[Thomas Jentzsch]

(I want Ewok Adventure and Lord of the Rings!)

Both are possible with F6 bankswitching after converting them a bit (I did Ewok already).

[Susuwatari]

@Burgertime: I could try to trace it but it will be a while because there's a total of 4 chips on the cart. I think there's 4 chips, I'll have to find that Burgertime cart and take it apart. Good thing the "2600 adapter" comes off easily with a couple small flat screwdrivers.

 

@Thomas - how hard is to convert other PB ROMs to use F6? I'd imagine not easy at all.

[Thomas Jentzsch]

@Thomas - how hard is to convert other PB ROMs to use F6?  I'd imagine not easy at all.

Not easy, but possible. It requires some time and knowledge.

 

I have written some simple programs which analyze the z26 trace file, checking which 2K bank combinations are possbile. In theory up to 2^3=8 combinations (one bank is fixed) are possible, but I was always (I did another one) able to reduce that down to 4. So I changed the bankswitching into F6 and put the 4 combinations into a 16K ROM.

 

That's all.