If so I would probably go with the second decoder of the LS139. (If I have enough space)
Thanks for the tip, but is there a Roms of 8 Mbytes?
Stacking 4x27c801 to build a 32Mbit cart.
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Re: Stacking 4x27c801 to build a 32Mbit cart.
The 27c080 is 8mbits, 1 mbyte.
If you want to use DIP EPROMs, the 27c080 is the biggest EPROM in a 32 pin package.
There is a larger dip eprom that is 42 pins 27c016 (16mbits or 2mbytes) that can be used.
The 27c016 can be configured through the byte pin to be 8 bit or 16 bit. 16 bit just means it has double the output data lines and all you need/want is 8 bit. This chip has a "byte" pin for this purpose.
Your only other option is a 27c322 42 pins EPROM. It's 32mbits and 16 bit only. The reason why it 16 bit only if because it had to use the byte pin as an address line. There are only so many pins available and they sacrificed the byte pin to add the extra address line A20. Now you might be thinking, wait a minute..... On the other chips, we talked about A21 being the 32mbit address line. True.
But when you have 16 bits, it's smaller than 8 bit but still the same. Wrap your mind around this...
16bit chip x 2mbytes = 32mbits. Highest address is A20
8bit chip x 4mbytes = 32 mbits. Highest address is A21
The 27c322 can be used with data converters discussed in a forum here not too long ago -- I'll post a link later... But essentially, with a few multiplexer chips, if converts the 16 bit EPROM into 8 bit.
Edit:
viewtopic.php?f=12&t=4877&start=45#p124330
If you want to use DIP EPROMs, the 27c080 is the biggest EPROM in a 32 pin package.
There is a larger dip eprom that is 42 pins 27c016 (16mbits or 2mbytes) that can be used.
The 27c016 can be configured through the byte pin to be 8 bit or 16 bit. 16 bit just means it has double the output data lines and all you need/want is 8 bit. This chip has a "byte" pin for this purpose.
Your only other option is a 27c322 42 pins EPROM. It's 32mbits and 16 bit only. The reason why it 16 bit only if because it had to use the byte pin as an address line. There are only so many pins available and they sacrificed the byte pin to add the extra address line A20. Now you might be thinking, wait a minute..... On the other chips, we talked about A21 being the 32mbit address line. True.
But when you have 16 bits, it's smaller than 8 bit but still the same. Wrap your mind around this...
16bit chip x 2mbytes = 32mbits. Highest address is A20
8bit chip x 4mbytes = 32 mbits. Highest address is A21
The 27c322 can be used with data converters discussed in a forum here not too long ago -- I'll post a link later... But essentially, with a few multiplexer chips, if converts the 16 bit EPROM into 8 bit.
Edit:
viewtopic.php?f=12&t=4877&start=45#p124330
Re: Stacking 4x27c801 to build a 32Mbit cart.
I've seen all this stuff in school but I forgot all of it and I'd like to master it once for all.
Thanks again for your help
p.s. Still, I thought the biggest Snes game was Tales of Phantasia 6Mb?
Thanks again for your help
p.s. Still, I thought the biggest Snes game was Tales of Phantasia 6Mb?
Re: Stacking 4x27c801 to build a 32Mbit cart.
Peccost wrote:I've seen all this stuff in school but I forgot all of it and I'd like to master it once for all.
Thanks again for your help
p.s. Still, I thought the biggest Snes game was Tales of Phantasia 6Mb?
I don't know of any bigger games than 6mB (Tales of Phantasia).
Re: Stacking 4x27c801 to build a 32Mbit cart.
There's 48 Mbit (ToP), and then there's 48 Mbit that's packed so tightly it takes a coprocessor to unpack it (Star Ocean, Street Fighter Alpha 2). The lookup tables inside the coprocessor aren't part of the ROM image as commonly understood, but they are on a component soldered to the PCB that contains ROM.
Re: Stacking 4x27c801 to build a 32Mbit cart.
tepples wrote:There's 48 Mbit (ToP), and then there's 48 Mbit that's packed so tightly it takes a coprocessor to unpack it (Star Ocean, Street Fighter Alpha 2). The lookup tables inside the coprocessor aren't part of the ROM image as commonly understood, but they are on a component soldered to the PCB that contains ROM.
True. I think he was just referring to games that were on a standard HiRom cart.