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The FF1 (FamiFlex) Mapper!

NOTE: THIS IS A WIP PAGE FOR A WIP PROJECT, THE INFO HERE MAY NOT BE UP TO DATE OR ACCURATE

So, some time ago I bought an old famiclone, and eventually I wanted to give a shot at playing some homebrew games on it (and even maybe make my own), so out of boredom and a desire for learning came the FF1 mapper!

Its a mapper that makes use of 74670 4x4 register chips (as I had a bunch of them lying around), and that can be configured to emulate many of the "bus-conflict" mappers that are commonly used in the homebrew scene, including NROM, UNROM, AxROM and UNROM 512. As well as many other possible configurations (including some not really present in any documented mapper).

MAPPER	n.ICs	PRG max(Kb)	PRG banking	CHR type	CHR max(Kb)	CHR banking	PRG RAM	Game Saves	Mirroring	Register
NROM (i000)	2	32	32f	ROM	8	8f	no	no	fixed V/H	-
UNROM (i002)	4	256	16+16f	RAM	8	8f	no	no	fixed V/H	----.PPPP
AxROM (i007)	4	128	32	RAM	8	8f	no	no	1-screen	---M.-PPP
BNROM (i034)	4	128	32	RAM	8	8f	no	no	fixed V/H	----.--PP
COLORDREAMS (i011)	?	128	32	ROM	128	8	no	no	no	fixed V/H
UNROM 512 (i030)	5-6	512	16+16f	RAM	32	8	no	yes (PRG FLASH)	fixed V/H or switch 1-screen or fixed 4-screen	MCCP.PPPP
FF1	2-4	512	32f or 32 or 16+16f or 16+16	RAM/ROM	32(RAM) or 128 (FLASH)	8f or 8 or 4+4f or 4+4	no	yes (CHR FLASH)	fixed V/H or switch 1-screen or fixed 4-screen	variable (see jumper setup)

Theory of operation

The FF1 presents one or two registers accessible by writing to ROM (note: this is a bus conflict mapper, thus the region of ROM you write to must contain the same value you are writing). The register(s) can be either 4 or 8 bit, with each half of the byte being a separate `670 4x4 register.

These registers in turn control the memory bank mapping of PRG and CHR, as well as mirroring while using single screen mode.

Parts

39SF040 512Kb Flash Memory, 1 or 2 depending if CHR Ram is used
62256 SRAM Standard 32K*8 memory, used for games with CHR Ram
74hc670 Register Chips; 0, 1, or 2 depending on the game
9pin ~3.3K to 10K resistor network Best value not currently determined
0805 smd decoupling caps (1 per chip)

Jumpers

FF1 uses a series of solder jumpers in the back of the board to customize it, these are where the flexibility part of the mapper comes in, as the board can be made to use a variety of different configurations:

Nametable Setup

The Famicom PPU is based around using 4 logic nametable screens, but it only contains enough internal VRAM to store 2 of them, an option exists to use cartridge RAM instead in order to enable the maximum 4 screens, and is supported by FF1:

2s/4s - Use 2 or 4 screens, must be set
/VRAM - Enables the VRAM inside the Famicom, this should be bridged unless 4 screen mode is being used

Finally when using 2 screen mode we must settle on a mirroring mode to use in order to fill up the 4 logical nametable screens, in that case one (and only one!) of the following jumpers must be set

Hm/Vm - Set mirroring to either fixed horizontal or vertical
1m/1m r.7 - Set scrolling to 1 screen, either fixed or set by bit 7
1m r.5/6 - Set scrolling to 1 screen, set by either bit 5 or 6
1m r.4 - Set scrolling to 1 screen, set by bit 4

1 screen mirror mode works by switching between 2 screens through the corresponding bit

Banking Setup

N/i30 - This sets whether bit 4 is used for CHR (N) or for PRG (i30), the latter setting is used in the UNROM 512 mapper (iNES 030)
B## - The number of banked regions to use. If set to 2, a second banking register will become available at the range $C000-$FFFF.
PRG R## - Should the PRG banked regions occupy all (1) or half (2) of the address space.
CHR B## - The number of banked regions to use for CHR memory

Finally we can decide which of the bits 5,6,7 are used for CHR banking:

4s/Br.5 - Use 4 mode or use bit 5
Br.6 - Use bit 6
Br.7 - Use bit 7

R1 and D1

These are odd components needed for when bit 4 is used for PRG mapping in a Mapper i30-like mode. D1 should be a standard 1n4 diode and R1 Should be a 4.7K resistor.

Example Configurations

NROM

32K PRG + 8K CHR

CHR Rom
No Register
Set jumpers /VRAM, 2s, N
Set Hm or Vm according to which mirroring type is used by the game.

AxROM

512K PRG (16x32K) + 8K CHRam

CHR Ram
Lo Registe + Hi Register
Set jumpers /VRAM, 2s, N, B# 1, PRG B# 2, 1m.r4

UNROM

256K PRG (16x16K) + 8K CHRam

CHR Ram
Lo Register
Set jumpers /VRAM, 2s, N, B# 1, PRG B# 1
Set Hm or Vm according to which mirroring type is used by the game.

UNROM 512

512K PRG (32x16K) + 32K CHRam (4*8K)

CHR Ram
Lo Register + Hi Register
D1 and R1
Set jumpers /VRAM, 2s, i30, B# 1, PRG B# 1, CHR B# 1
Set Hm or Vm according to which mirroring type is used by the game

FF1

A "Maxed-Out" setup for my own homebrew use.

512K PRG (16x16K(a) + 16x16K(b)) + 128K CHRom (16x4K(a) + 16x4K(b))

CHR Rom
Lo Register + Hi Register
Set jumpers /VRAM, 2s, i30, B# 2, PRG B# 2, CHR B# 2, r.4 to r.7*
Set Hm or Vm according to which mirroring type is used by the game.