Microcontroller for switching address pins LoROM and HiROM

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Kayumba
Posts: 246
Joined: Sun Mar 01, 2020 2:36 am

Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

Hi,
Do somebody know if there is some chip that can control input/output to be able to do some switching for address pins between LoROM and HiROM ?

PS: Sad to see that forum is seams to be like dead...
No more answers, no one visiting this website :(
lidnariq
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Joined: Sun Apr 13, 2008 11:12 am

Re: Microcontroller for switching address pins LoROM and HiROM

Post by lidnariq »

No microcontroller, no. Ordinary 74xx series multiplexers can work, however.
Kayumba
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

Can you share schematic ?
Or some example for one adress pin.
Kayumba
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Joined: Sun Mar 01, 2020 2:36 am

Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

Can I use 2:1 Multiplexer like NC7SV157P6X ?
Image
If yes, then I need to have 7 like that :cry: (for each address pin that changes between Hi/Lo).
But with only one switch button I can setup all 7 address pins for Hi or Lo.
What do you think?

74157 seam's to have 4 multiplexers 2:1
Image
Image
Do you know if there is one with 8 multiplexers 2:1 ?

Take a look please and tell me if it's have to look like that?
If yes, so I just need to use 2 multiplexers to control 7 outputs.
Image
lidnariq
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by lidnariq »

Yes, you could use two '157s this way.
Kayumba
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

lidnariq wrote: Thu Jan 27, 2022 12:54 pm Yes, you could use two '157s this way.
Thanks :wink:
Kayumba
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

lidnariq wrote: Thu Jan 27, 2022 12:54 pm Yes, you could use two '157s this way.
Do you know one with 8 multiplexers 2:1 ?
lidnariq
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by lidnariq »

I don't already know of one, but many online storefronts should let you search.
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Ben Boldt
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Ben Boldt »

An “octal bus switch” will probably be unusual and expensive. It would take at least 27 pins if I count right. (3pins x 8 multiplexers, 5V, GND, select) In general, pretty unusual to find logic chips in a big package like that. You will probably be a lot better off using 2 cheap/common ‘157 chips.

How would you plan to control these multiplexers? Are you planning to have the snes itself do itsomehow, or using a jumper/switch inside the cart? If you are using a jumper, you may as well just use 8 jumpers and not use any multiplexer at all. You could even use a 3x8 pin header and a 2x8 jumper block. Move the jumper block to select hi-rom vs lo-rom.
Kayumba
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

Ben Boldt wrote: Sat Jan 29, 2022 10:10 am An “octal bus switch” will probably be unusual and expensive. It would take at least 27 pins if I count right. (3pins x 8 multiplexers, 5V, GND, select) In general, pretty unusual to find logic chips in a big package like that. You will probably be a lot better off using 2 cheap/common ‘157 chips.

How would you plan to control these multiplexers? Are you planning to have the snes itself do itsomehow, or using a jumper/switch inside the cart? If you are using a jumper, you may as well just use 8 jumpers and not use any multiplexer at all. You could even use a 3x8 pin header and a 2x8 jumper block. Move the jumper block to select hi-rom vs lo-rom.
Hi Ben bolt,

Thanks for your advice and help.
Well…
Jumpers, jumpers, jumpers…
So yes, it’s the most be a chipper method to change between two maps.
But I want to try with multiplexers.
I think it’s more confortable to use just one « switch »on the board or only one jumper and chip that will control all for me.
About SNES and how it can be detect by SNES I don’t know how can it be do.
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Ben Boldt
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Ben Boldt »

My opinion, you are adding something more complex than it needs to be. There should be a mechanical way to do this that does not introduce extra gates into your circuit.

You could do 2 ROM chip outlines, which can overlap. One outline wired as hirom, the other lorom. You make the selection by which one you install the ROM chip into.

It makes sense that multiplexers would work, I am not saying that the idea won’t work. I am saying you will have a more reliable and less expensive product if it is less complicated. For example, nothing can go wrong with your multiplexers if they don’t exist.

Why you want multiplexers:
- you envision 1 mechanical switch in your circuit to select hi/lo ROM, and you are attached to that idea.

Why you don’t want multiplexers
- extra complexity
- extra cost
- extra effort soldering
- unforeseen issues arise with new circuit
- new point of failure that doesn’t need to exist
Kayumba
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by Kayumba »

Thx for your opinion ben.
It’s very intresting to know what other users are thinking.

For me, with or without multiplexers ,
Use Jumpers or reserved place on the board.
you can always find advantages and disadvantages.
Some users like one design other choose something else.
Of course if you choose to do a cheaper design, so yes, you should design circuit with less extra chips on it.

But if like in my case,
I would like to have one PCB that will be ready to use, with all chips already soldered on it (with SMT service).
After what you will just need to setup your board with one or two switches on it, and program your Eprom or flash chip.
Of course if the final price of this one « extra board » will cost to me 10$ or more…
So yes, better to spell a time with solder iron :)
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aquasnake
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Re: Microcontroller for switching address pins LoROM and HiROM

Post by aquasnake »

The bank address lines of lorom is misaligned by 1 bit from that of hirom. You only need to share 7 bits and route 1 bit, and then convert the scrambled address to a new ROM through some appropriate tool
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