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Apple ][ ROM Card

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David_M

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Joined
Oct 1, 2016
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Location
Melbourne, Australia
My prototype boards arrived today for the new card I'm working on.
The address decode/remap code for the GAL still needs to be written, but I should have production boards ready to ship in 2 or 3 weeks.

20180924_151202[1].jpg
 
The GAL is complete and working. Any one of six F8 images or the motherboards F8 ROM can be selected to work with either Applesoft or integer basic on the card.
DMA daisy chaining is fully supported and it is 100% upwardly compatible with the Apple ROM card.

One of the F8 images is a dead boot diagnostic that can boot with faulty RAM.

Bare boards will be US$10 plus $3.50 shipping PM me for my paypal details.
If anyone was an assembled board or a kit of parts PM me also.
 
Last edited:
mwillegal said:
note that ATMEL EEPROMs sometimes have trouble working with a 6502 address bus.

http://www.willegal.net/blog/?p=2785

regards,
Mike Willegal
Click to expand...

I had an issue with the GAL in the Saturn 128k reboot card, it required a pullup resistor to get the DMA daisy chaining to work. Lattice GAL's worked fine though.
The ROM card works fine though. Both of the prototypes I assembled use an Atmel 28C256. I put an Atmel GAL in one and a Lattice GAL in the other and both works fine.
I was going to include the ability to write to the EEPROM but didnt work and only served to corrupt the ROM image when booting so I pulled that option from the production boards. Maybe I should have tried some other brands of EEPROM.
 
With the Superproto, I found I had an issue with the write line and chip select going active during boot causing a spurious write. I was able to fix it with a GAL change, though at this moment, I can't remember exactly what that was. Be cautious about using the Atmel EEPROMs, they are definately marginal. I know of at least three different designers that encountered issues with 6502 address bus compatibility. I seem to recall that someone told me he was able to delay one of the Apple II signals in order to make it work reliably. Maybe your design already has this kind of delay built in.

best regards,
Mike Willegal

David_M said:
I had an issue with the GAL in the Saturn 128k reboot card, it required a pullup resistor to get the DMA daisy chaining to work. Lattice GAL's worked fine though.
The ROM card works fine though. Both of the prototypes I assembled use an Atmel 28C256. I put an Atmel GAL in one and a Lattice GAL in the other and both works fine.
I was going to include the ability to write to the EEPROM but didnt work and only served to corrupt the ROM image when booting so I pulled that option from the production boards. Maybe I should have tried some other brands of EEPROM.
Click to expand...
 
The last thing I need is random writes when the cards will potentially be used by people that don't have the ability to reprogram the ROM. So it is probably for the best that I dropped the option.
 
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