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SkalTura

PixelPast bankswitch card

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Anyone any experience with the bankswitch cartridge from PixelPast (http://www.grandideastudio.com/pixels-past/)...?

 

Made one using the F8 program in the PLD, and Ms.Pacman (8k) but all I get is a black screen.

There is no mention in the description of the card, but I wonder if I should fill the 27C256 with the same game multiple times ?

Now I just programmed the 27C256 with 1 time Ms.Pacman, and filled the blank space with "FF", just like I would do on any other Eproms.

 

Anyone ?

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52 minutes ago, SkalTura said:

Now I just programmed the 27C256 with 1 time Ms.Pacman, and filled the blank space with "FF", just like I would do on any other Eproms.

If I'm understanding correctly the "F8" pld source code from the page you linked, pin 26 (not connected on a 2764, address A13 on a 27128 and 27256) is always low, while pin 27 (/PGM on a 2764 and 27128, A14 on a 27256) is always high.

pldcode.thumb.png.8e6790194d7dd9c36b01d8027a2a626c.pngf8schem.thumb.png.1a048d45af960c9fa2cb002a4e7ef007.png

 

Which means that if you're using a 27256 for a F8 game, the rom must be burned starting from address 4000 (hex value).
So you'll have 16k of unused space, then the 8k rom, then another 8k of unused space.

 

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Just as a rule of thumb, I always mirror up the data on an (E)EPROM, when using a larger one than needed. It had never failed me so far, and even works if the most significant address bit(s) is/are floating. And I've seen guys trying to pull lines up/down using resistors to match the part of the EPROM they use. In theory it should work, practically they've fallen back to mirroring the data to get it stable.

 

Pro-tip: look for some cheap 27SF256 EEPROMs. They can be used as a drop-in replacement for the 27C256, but can be reprogrammed without the UV-light step, similar to a flash chip. For these I've also got boards using zif-sockets for easy changing of the chip. One of 4k, F8, F6, and F4 each.

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8 hours ago, SvOlli said:

Pro-tip: look for some cheap 27SF256 EEPROMs. They can be used as a drop-in replacement for the 27C256, but can be reprogrammed without the UV-light step, similar to a flash chip. For these I've also got boards using zif-sockets for easy changing of the chip. One of 4k, F8, F6, and F4 each.

I have a UV box, so I don't mind erasing the chips.

Usually keep the failed or old Eproms in a separate box, and erase then all at ones when I have 10 or so...

 

I'm actually working on a cartridge that supports multiple F8 games, but wanted to try the PLD cart first to figure out if that was useful to me.

So eventually I will indeed use a EEprom, maybe 4M or 8M so store several 8k games.

 

Work in progress...  ;-)

Edited by SkalTura

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Don't know if anyone ever thought of this, but just in case... Here are my findings...

 

The PixelPast bankswitch card works as expected, using the F8 file for 8k games in the PLD, and a 27C256 Eprom.

Since only A12 on the Eprom is used for bankswitching, A13 and A14 (as mentioned in the PLD file (thank you alex_79)) are only used to select where the game is started from.

So I loaded 4 different 8k games in the Eprom and disconnected A13 and A14 from the PLD.

Connecting A13 and A14 to either +5V or to ground, selects one of the 4 games.

 

Games in the Eprom, in this order were:

- Ms. Pacman

- E.T.

- Galaxian

- StarGate

 

Worked perfectly for Ms. Pacman and E.T.

Galaxian started scrambled.

SartGate didn't start at all.

 

But to be honest, I tested this on a breadboard with about 50 wires connecting the PLD to the Eprom and the Atari connector, so a bit of instability was to be expected.

I will make a PCB for it soon for more testing.

 

And I guess it will also work for a F6 (16k) bankswitch card, selecting the games with only A14 (and A15 if you use a 27C512)

 

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Designed a PCB that can be used for 2k/4k games, but also 8k, 16k and 32k games.

Using the jumpers, you can select what type of bankswitching you want to use (F8/F6/F4, or no bankswitching).

And with the rest of the jumpers, you can select different games.

 

It uses a 1024k Eeprom (29F010 in my case), and a 20V8 PLD just like the PixelPast cartridge.

 

So if you want to use 16k games for example, put jumper F8 and F6 sideways.

The A12 and A13 signals from the PLD will then go to the Eeprom.

The other jumpers can then be put to either up/down (+5V or Ground) for selecting 8 different games.

 

If you want to use it for normal 4k games, use all jumpers to either +5V or Ground for selecting 32 games.

Bankswitching is then not used, so the output of the PLD is only used for the Chip Enable signal.

 

NOTE:  Only tested with an (unstable) breadboard setup, so I will need to make the PCB to see if this is indeed a stable working solution...

NOTE:  Not sure if the PCB fits in all cartridge cases, but it does fit in the one I have. It think it was the case from Asteroids, but its been so long ago that I'm not sure of this.

 

 

cartridge7.jpg

cartridge8.jpg

Edited by SkalTura
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The unstable breadboard setup with many many many wires was working fine.

Sometimes wiggling the wires was needed, but E.T (8k) started without much trouble.

Once the wires were stable, I've restarted the Atari about 20 times and it always started E.T.

cartridge3.thumb.jpg.ff6a3729de2f4a26b773fbe0d70ef513.jpg

 

So I designed the PCB for it, as shown in the previous post and had the PCB made.

Received the PCB's a few days ago, and soldered one together for testing (don't mind the "F6", that was from a different test).

cartridge10.thumb.jpg.9c627131c8832915471ef0f8d045542c.jpg

But for some unknown reason it doesn't work at all, and I can't seem to figure out why.

I've even tried it with the F8 PLD and 27C256 Eprom that were on the breadboard setup, but nothing.

So I stuck the PLD and Eprom back on the breadboard, and it started first time...

 

Super annoying !!

Back to the drawing board  😞

 

 

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Did some measuring, turns out that the PCB's are not correctly made.

My design is correct, but for some reason the PCB manufacturer didn't make all traces going to the Eeprom  😞

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Did some further testing, and it seems to work fine for most ROM's.

Even mixing up different sizes works for some ROM's.

 

Let me know if someone is interested, then I will share the Gerber files for PCB making...

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On 11/12/2021 at 5:38 PM, cbelcher said:

Interested!

Cool  ;-)

Here are the Gerber files.

Also made a short video on YouTube, so you can see it working.


Note:  Only tested with a few games (because my machine is PAL, and most of the games I downloaded are NTSC), but it seems to work fine for the ones I used for testing...

 

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8 hours ago, cbelcher said:

Ok and burn the desired F4 F6 or F8 GAL file from 

http://www.grandideastudio.com/pixels-past/

Correct?

 

You said if there is no bankswitching the PLD is only used for CE chip enable - does it matter which file is used?

Yes, use the PLD/GAL file from PixelPast.

If you play only 4k games (for 2k games, double them), you only need the CE signal from the PLD, so then it doesn't matter what file you use, since the A12, A13 and A14 lines (sideways jumpers F8, F6 and F4) will be jumpered to either +5v or GND, and not to the PLD anymore.

And you don't have to use a 1M Eeprom, you can also use a 27C256 or 27C512 is you have hem. Just place it as marked on the silkscreen...

 

eeprom-silkscreen.jpg.e3aa1c76169b575c308bc2d7e7671ee2.jpg

 

Edited by SkalTura

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