Converting a 16bit eprom to run as 8bit
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Converting a 16bit eprom to run as 8bit
I stumbled across this:
http://www.jammaplus.co.uk/forum/forum_ ... =starfox-2
Could someone please explain how on earth you convert a 16 bit eprom to 8 bit? And is it simple?
http://www.jammaplus.co.uk/forum/forum_ ... =starfox-2
Could someone please explain how on earth you convert a 16 bit eprom to 8 bit? And is it simple?
Re: Converting a 16bit eprom to run as 8bit
I'm assuming that you just ignore the upper 8 bits of each word (leave unconnected), and adjust the image you send to the programmer.
Re: Converting a 16bit eprom to run as 8bit
Didn't magno perfect using the 27C322 chips before? I know he has eluded to it a number of times that he has a working design on how to wire them to a cart. Drakon, if you search through this forum I believe there is some info about it.
- mikejmoffitt
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Re: Converting a 16bit eprom to run as 8bit
I'm a little confused - this example with Star Fox 2 isn't supposed to involve what you are talking about, is it? I see a 16-bit EPROM on his SF2 PCB, unless you are talking about his other board.
He probably just has the upper 8 lines ignored. If it's for use in an NES/FC cartridge, you could put your CHR data in the upper 8 bits and your PRG data in the lower 8 bits to make a merged 16-bit file to put on a single EPROM, though be sure to mirror your data to fill extra space (I.E. if you have an 8MBit (1MByte) 16-bit ROM, 512KByte PRG and 128KByte CHR, CHR must be copied four times to make 512KByte).
If it is for an SFC / SNES cartridge, what would you be doing with an 8-bit ROM?
He probably just has the upper 8 lines ignored. If it's for use in an NES/FC cartridge, you could put your CHR data in the upper 8 bits and your PRG data in the lower 8 bits to make a merged 16-bit file to put on a single EPROM, though be sure to mirror your data to fill extra space (I.E. if you have an 8MBit (1MByte) 16-bit ROM, 512KByte PRG and 128KByte CHR, CHR must be copied four times to make 512KByte).
If it is for an SFC / SNES cartridge, what would you be doing with an 8-bit ROM?
Re: Converting a 16bit eprom to run as 8bit
This doesn't make sense. Why would you put CHR data into the upper bytes?mikejmoffitt wrote:If it's for use in an NES/FC cartridge, you could put your CHR data in the upper 8 bits and your PRG data in the lower 8 bits to make a merged 16-bit file to put on a single EPROM.
You're asking why you would use an 8-bit ROM in a SNES cartridge? Because it has an 8-bit bus?If it is for an SFC / SNES cartridge, what would you be doing with an 8-bit ROM?
Re: Converting a 16bit eprom to run as 8bit
Its competitor has a 16-bit bus. Genesis does what Nintendon't.blargg wrote:You're asking why you would use an 8-bit ROM in a SNES cartridge? Because it has an 8-bit bus?
Re: Converting a 16bit eprom to run as 8bit
There's a byte pin to select bit size, guys.
- TmEE
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Re: Converting a 16bit eprom to run as 8bit
But not on a 27C322.
On other chips there is, and it turns D15 into an additional address pin, usually called A-1. D8 to D14 will do nothing in that mode.
On other chips there is, and it turns D15 into an additional address pin, usually called A-1. D8 to D14 will do nothing in that mode.
- mikejmoffitt
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Re: Converting a 16bit eprom to run as 8bit
Christ, I was tired and that makes no sense, disregard that. That would only work if you were for some reason reading from PRG the exact same address as CHR at all times.blargg wrote:This doesn't make sense. Why would you put CHR data into the upper bytes?mikejmoffitt wrote:If it's for use in an NES/FC cartridge, you could put your CHR data in the upper 8 bits and your PRG data in the lower 8 bits to make a merged 16-bit file to put on a single EPROM.
Re: Converting a 16bit eprom to run as 8bit
So this whole thread is for nothing?3gengames wrote:There's a byte pin to select bit size, guys.
- nintendo2600
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Re: Converting a 16bit eprom to run as 8bit
Ya D15 becomes A0 and you shift the rest of the addy lines +1.TmEE wrote:But not on a 27C322.
On other chips there is, and it turns D15 into an additional address pin, usually called A-1. D8 to D14 will do nothing in that mode.
- nintendo2600
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Re: Converting a 16bit eprom to run as 8bit
Also does anyone here know "AndrewC" aka "Pootle" on other forums?
I really wanna get in touch with him about buying some of his 27c160 and 27c322
adaptor boards for the SNES. Hell if I could even just get the egale files I'd be
a happy man and I would just get a batch done myself.
I can design the one for use with the 27c160 in 8bit mode but I'm not ninja
enough to design the one with the 27c322 and the 245's and 139. That one
I would love to buy\and or get some made.
I really wanna get in touch with him about buying some of his 27c160 and 27c322
adaptor boards for the SNES. Hell if I could even just get the egale files I'd be
a happy man and I would just get a batch done myself.
I can design the one for use with the 27c160 in 8bit mode but I'm not ninja
enough to design the one with the 27c322 and the 245's and 139. That one
I would love to buy\and or get some made.