Mapper 472 / NROM-383 and NROM-368

[akerasoft]

** Update Mapper number changed to 474. Also sample ROMs with hello world. (Previous suggested mapper number was 472).

I've created a mapper that maps 0x4020 to 0xFFFF to PRG ROM.
I called it Akerasoft Mapper 474.
It maps more than NROM-368. But an NROM-368 is also planned. So the original one is NROM-383 (rounding down).

My prototype uses FLASH memory but is designed to be programmed before soldering and is not reflashable.

https://www.nesdev.org/wiki/NROM-368

My design however is this 64KB of ROM space:
Bank 0:
Memory 0x0000 - 0x3FFF (empty or ignored, all zeros?)
Bank 1:
Memory 0x4000 - 0x401F (empty or ignored, all zeros?)
Memory 0x4020 - 0x7FFF (PRG)
Bank 2:
Memory 0x8000 - 0xBFFF (PRG)
Bank 3:
Memory 0xC000 - 0xFFFF (PRG)

Mapper 472 submapper 0 - 0x4020 - 0xFFFF (NROM-383)
Mapper 472 submapper 1 - 0x4800 - 0xFFFF (NROM-368)

For .NES File my design is this 48KB of ROM space:
Bank 0:
Memory 0x4000 - 0x401F (empty or ignored, all zeros?)
Memory 0x4020 - 0x7FFF (PRG)
Bank 1:
Memory 0x8000 - 0xBFFF (PRG)
Bank 2:
Memory 0xC000 - 0xFFFF (PRG)

hello_world_nrom_383.nes

Hello World - Mapper 474 - Submapper 0 sample - NROM-383

(56.02 KiB) Downloaded 2 times

hello_world_nrom_368.nes

Hello World - Mapper 474 - Submapper 1 sample - NROM-368

(56.02 KiB) Downloaded 2 times

Repos for the above built ROMs:
https://github.com/Akerasoft/hello_world_nrom_383
https://github.com/Akerasoft/hello_world_nrom_368

[aquasnake]

Most coders are detached from reality because they only have software thinking rather than hardware thinking.

For you, $4020- $FFFF appears to have a wider addressing range than $4800- $FFFF. However, in actual design, the former requires a 16 bit numerical comparator, while the latter only requires A [11.. 15] as inputs to a chip of quad-NAND gates.

Therefore, you would understand why only NROM-368 is meaningful to implement NROM rather than over 368Kbits

[akerasoft]

Actually. Both designs use an OR gate.
NROM-383 (uses 8 input OR gate, plus an extra 2 input Or gate).
NROM-368 (uses 4 input OR gate)

I tried to think about the comparator. I was not sure if that would actually work.

[NewRisingSun]

Can you make it mapper 474, please? I have assigned mapper 472 and 473 for some multicart mappers already, but failed to update the wiki in time.

[akerasoft]

Sure, it can be Mapper 474. Can the wiki be updated so that I don't have to change the number again?

[NewRisingSun]

done

[aquasnake]

Actually. Both designs use an OR gate.
NROM-383 (uses 8 input OR gate, plus an extra 2 input Or gate).
NROM-368 (uses 4 input OR gate)

I tried to think about the comparator. I was not sure if that would actually work.

8 input OR gate is 5 times the price of quad 2-input NAND

Comparator has better versatility, but is rarer and more expensive in the market

[Fisher]

8 input OR gate is 5 times the price of quad 2-input NAND

Comparator has better versatility, but is rarer and more expensive in the market

Can't this be made with 8 diodes and a resistor?
If so, would that be cheaper?

[akerasoft]

.NES File Format - Mapper 474.
8 KB CHR
48KB PRG (3 banks)
Bank 0 - 0x4020 or 0x4800 to 0x7FFF (prepadded with zero's)
Bank 1 - 0x8000 to 0xBFFF
Bank 2 - 0xC000 to 0xFFFF

To make ROM bin files from NES file or make NES file from ROM bin files.
https://github.com/Akerasoft/Mapper474ROMTool

To resize an NROM to Mapper474
https://github.com/Akerasoft/NROMToMapper474

After having a Mapper474 .NES file you can HEX edit.

[akerasoft]

8 input OR gate is 5 times the price of quad 2-input NAND

Comparator has better versatility, but is rarer and more expensive in the market

Can't this be made with 8 diodes and a resistor?
If so, would that be cheaper?

It would be 9 diodes. Not sure about the price.

[aquasnake]

9 diodes can gate $4020-$403F, but I'm not sure if they can gate >=$4020

[akerasoft]

9 diodes can gate $4020-$403F, but I'm not sure if they can gate >=$4020

An AND gate is used for >=$4000, adding (a 9 input or gate) or 9 diodes changes it to >=$4020.

[akerasoft]

Update: ROMs and Repos for the sample ROMS was added.