Bandai FCG board

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Bandai FCG boards are used largely by Bandai for Dragon Ball and Gundam games, as well as a few others. One IREM title uses it as well.

These boards contain one of Bandai's FCG mapper chips.

Hardware: PRG ROM (16 KiB banks, one switchable and one fixed), CHR ROM (1 KiB banks), no PRG RAM, optional I²C EEPROM (24C02 or 24C01).

Four mappers are used to describe these boards

  1. iNES Mapper 016 is intended for use with boards which contain a 24C02 256-byte serial EEPROM (but may contain none)
  2. iNES Mapper 153 is a rarely used assignment for a customized board with no EEPROM and SRAM in its place.
  3. iNES Mapper 157 is used for the Datach Joint ROM System which has a barcode reader in lieu of SRAM.
  4. iNES Mapper 159 is intended for use with boards which contain a 24C01 128-byte serial EEPROM

You may encounter ROMs with the mapper assignments mixed up. There used to be no distinction when 016 was first assigned. The distinction was introduced later to distinguish the 128-byte boards from the 256-byte or no-EEPROM boards. In NES 2.0 format, only 157 differs, because the "battery backed PRG RAM size" field completely disambiguates those boards, though emulators MAY display a warning when the RAM size field is abnormal for a given mapper.

FCEUX does not emulate the EEPROM. It seems that returning 0x00 from EEPROM registers suffices to get most games booting.

Ports

There are actually two significantly different versions of the hardware:

  • Bandai's FCG-1 and FCG-2 only mirror these ports from $6000-$7FFF, and do not support an external EEPROM (or RAM)
  • Bandai's LZ93D50 (sometimes referred to as "FCG-3") only mirror these ports from $8000-$FFFF, and the serial EEPROM read port is mirrored across the entire range from $6000-$7FFF.
    • The Datach system includes its own 24C02, and at least one external cartridge also provides a 24C01. The two EEPROMs are clocked separately, but share the data line.

To enable mapper 16 to support both LZ93D50 games with or without EEPROM as well as FCG-1 and -2 games, an emulator should mirror the mapper's writeable ports across all of $6000-$FFFF, and the readable EEPROM input register from $6000-$7FFF.

For mapper 153 (with SRAM), the writeable ports must only be mirrored across $8000-$FFFF.

Mappers 157 and 159 do not need to support the FCG-1 and -2 and so probably should only mirror the ports across $8000-$FFFF.

  • $8000-$8007: Select 1024 byte CHR bank at $0000, $0400, ..., $1C00
    • But not for the Datach system, which instead only provides 8 KiB unbanked CHR RAM. Instead, the Datach system connects what would be CHR A10 to the external serial EEPROM clock line, so all four must be written with the same value to prevent incorrect traffic during rendering.
    • Also not for BA-JUMP2, which uses CHR A10 as PRG A18.
  • $8008: Select 16384 byte PRG bank at $8000 (the last bank is fixed at $C000)
  • $8009: Mirroring (0: vertical; 1: horizontal; 2: 1-screen $2000; 3: 1-screen $2C00)
  • $800A: IRQ control (0: pause; 1: count; any write acknowledges)
  • $800B: Low 8 bits of IRQ counter
  • $800C: High 8 bits of IRQ counter
  • $800D: EEPROM write (but not on FCG-1 or FCG-2)
    • BA-JUMP2 uses the I²C SCL bit as an additional enable for the PRG RAM.

When enabled, IRQ counts down by 1 every CPU cycle. /IRQ goes low when the counter goes from $0001 to $0000, and it goes high when $800A is written. The counter is not reloaded after IRQ; it'll fire once every 65536 cycles unless paused or reloaded with $800B/$800C writes.

Any read from $6000-$7FFF appears to read the EEPROM.

EEPROM appears to be laid out like this: 

7  bit  0  $800D: EEPROM control
RDC. ....
|||
||+-------- I²C SCL (Datach: internal EEPROM only)
|+--------- I²C SDA
+---------- Enable Read

7  bit  0  $6000-$7FFF: EEPROM or Barcode read
xxxE Bxxx
|||| ||||
+++|-|+++- Open bus
   | +---- Data out from Barcode reader (or open bus)
   +------ Data out from I²C EEPROM

Some patterns observed in the games' save code:

  • Start I/O: $00 $40 $60 $20 $00
  • Write 0 bit: $00 $20 $00
  • Write 1 bit: $00 $40 $60 $40 $00
  • Acknowledge: $00 $20 $A0 Read $00
  • Read bit: $60 $E0 Read $40
  • Stop I/O: $00 $20 $60 $40 $C0

Just use the datasheets for the 24C01 and 24C02 they used when implementing the EEPROM:

  • 24C01, has no device address/uses device address as memory address: Xicor, Atmel
    • The 24C01 is NOT little endian, despite what Disch wrote below. This is due to a mistake at Bandai, not a deviation from the datasheet.
  • 24C02, with device address: Xicor, Atmel

Disch's notes

Below, Disch was unfamiliar with I²C, so a number of his comments are solely from the point of view of someone unfamiliar with it. 

 Here is a lightly-edited version of Disch's original notes:
 ========================
 =  Mapper 016          =
 =       + 153          =
 =       + 159          =
 ========================
 
 aka
 --------------------------
 Bandai (something or other)
 
 
 Example Games:
 --------------------------
 Dragon Ball - Dai Maou Jukkatsu      (016)
 Dragon Ball Z Gaiden                 (016)
 Dragon Ball Z 2                      (016)
 Rokudenashi Blues                    (016)
 Akuma-kun - Makai no Wana            (016)
 Famicom Jump II: Saikyou no 7 Nin    (153)
 Dragon Ball Z - Kyoushuu! Saiya Jin  (159)
 SD Gundam Gaiden                     (159)
 Magical Taruruuto Kun 1, 2           (159)
 
 
 Three Mappers:
 ---------------------------
 016 and 159 are mapped the exact same way.  Registers are all the same and whatnot.  And in fact, for a
 while, both mappers were assigned the same mapper number (016).  Therefore, you may come across mapper 159
 games that are still marked as mapper 016.
 
 The difference between the two is in the EEPROM.  These mappers don't have traditional SRAM (I couldn't tell
 you why).  Instead, they have an I²C EEPROM that has to be written to one bit at a time, resulting in very 
 strange-seeming register writes.
 
 Mapper 016 has 256 bytes of EEPROM, and is accessed high bit first
 Mapper 159 has 128 bytes of EEPROM, and is accessed low bit first
 Mapper 153 (as far as we know used exclusively for Famicom Jump II: Saikyou no 7 Nin) has SRAM instead of an EEPROM.
 
 For further details, see the section at the bottom.
 
 Apart from save mechanism, the mappers are 100% identical in function.
 
 
 Notes:
 ---------------------------
 Since there's EEPROM, there's no SRAM (EEPROM is used to save games).
 
 
 Registers:
 ---------------------------
 
 Range,Mask:   $6000-FFFF, $000F
 
 Note:  below regs are listed as $800x, but note they also exist at $6000-7FFF
 
 
   $8000-8007:   CHR Regs
   $8008:        PRG Reg (16k @ $8000)
 
   $8009:  [.... ..MM]   Mirroring:
     %00 = Vert
     %01 = Horz
     %10 = 1ScA
     %11 = 1ScB
 
   $800A:  [.... ...E]   IRQ Enable (0=disabled)
   $800B:                Low 8 bits of IRQ Counter
   $800C:                High 8 bits of IRQ Counter
 
   $800D:  EEPROM I/O
 
 another note:   since PRG is mapped to $8000-FFFF, EEPROM I/O reg can only be read via $6xxx or $7xxx.  To my
 knowledge no other registers are readable.  It also appears that reading from *ANY* address in $6xxx-7xxx
 will read the EEPROM I/O reg.  Rokudenashi Blues will poll $7F00 and will wait for bit 4 to be 0 before
 continuing (so if you're giving open bus @ 7F00, the game will deadlock)
 
 CHR Setup:
 ---------------------------
 
       $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
     +-------+-------+-------+-------+-------+-------+-------+-------+
     | $8000 | $8001 | $8002 | $8003 | $8004 | $8005 | $8006 | $8007 | 
     +-------+-------+-------+-------+-------+-------+-------+-------+
 
 
 PRG Setup:
 ---------------------------
 
       $8000   $A000   $C000   $E000  
     +---------------+---------------+
     |     $8008     |     { -1}     |
     +---------------+---------------+
 
 
 
 IRQs:
 ---------------------------
 IRQs are nice and simple.
 
 When enabled, the 16-bit IRQ counter counts down every CPU cycle, wrapping from $0000->FFFF.  When the
 counter makes the transition from $0001->$0000, an IRQ is generated.
 
 When disabled, the IRQ counter does not count.
 
 Any write to $800A will acknowledge the IRQ
 
 $800B and $800C change the IRQ counter directly -- not a reload value.
 
 
 EEPROM:
 ---------------------------
 EEPROM is a real nightmare.  Nobody knew exactly how it worked -- but by examining the game code,
 patterns surface.  Games do a series of extremely cryptic writes to $800D, and occasionally read a single
 bit from $800D.  By examining some logs I made of the games I've noticed a small bit of patterns which I
 list below, along with my guess as to what the game is attempting to do by performing that pattern:
 
 
   write $00
   write $40
   write $60     Start I/O
   write $20
   write $00
 
   write $00
   write $20     Output '0' bit
   write $00
 
   write $00
   write $40
   write $60     Output '1' bit
   write $40
   write $00
 
   write $00
   write $20
   write $A0    I have absolutly no clue
   Read
   write $00
 
   write $60
   write $E0    Read a single bit
   Read
   write $40
 
   write $00
   write $20
   write $60    Stop I/O
   write $40
   write $C0
 
 
 These likely aren't the only patterns that games perform.  I recall seeing occasional writes of $80 and
 other stuff thrown in there in some games.  Also -- not all games follow this pattern, so looking for these
 specific writes will not work for at least one other game.
 
 It seems that only bits 5-7 of the written value are relevent (hereon, they will be referred to as D5 - D7).
 Bit 4 ($10) is the only significant bit when read.  Other bits are most likely open bus.
 
 
 When writing bytes to EEPROM, games will generally perform 8 "output" patterns (either output 0 or output 1,
 depending on the bits it wants to write), followed by a 9th output pattern, which I would assume finalizes
 the write and/or possibly moves the 8 bits from a latch to EEPROM.
 
 When reading bytes, games will generally perform 8 "read" patterns, followed by a single output pattern
 (which I would assume finalizes the read).
 
 Sometimes when the game is writing bits, it's writing data to be stored on EEPROM, and other times it's
 setting the desired EEPROM address and/or read/write mode.  Knowing which it's doing involves keeping track
 of the state it's currently it and what it has done last, etc, etc.
 
 But again -- nobody *really* knows how it works.  The method I've employed in my emu is outlined below -- and
 it appears to work for every game I've tried, but I *KNOW* it's not accurate.  But, short of some hardware
 guru acquiring a handful of these carts and doing a thorough RE job, that's about the best anyone can do.
 
 
 Emulating EEPROM:
 -----------------------
 
 SUPER FAT IMPORTANT NOTE:  This is just the method of EEPROM emulation I employ in my emu.
 
      ***THIS IS NOT HOW THE ACTUAL HARDWARE WORKS***
 
 Do not use this as a final word or anything -- this is simply the product of lots of guesswork, speculation,
 and trial and error.
 
 
 D5 appears to be the "trigger" bit, and D6 appears to be the "signal" bit.  I have no clue what D7 does, and
 ignoring it completely has worked for me (though I'm sure it does have some purpose).  "Commands" are sent
 by toggling D5 (0->1->0).  Two states of D6 are observed -- one when D5 rises (0->1), and one when it falls
 (1->0).  Using these two observed states, you get 4 possible commands.  The command is sent when D5 falls.
 
 Example:
 
          byte  D6 D5 
   write: $00    0 0
   write: $40    1 0
   write: $60    1 1  <--  D5 rise:    D6=1
   write: $40    1 0  <--  D5 fall:    D6=1, command "1,1" sent here
   write: $00    0 0
 
 The above sequence would issue a "1,1" command.
 
 Commands:
 
   Name     rise,fall       example write sequence
   ------------------------------------------------
   Write 0     0,0          $00, $20, $00
   Write 1     1,1          $00, $40, $60, $40, $00
   Open        1,0          $00, $40, $60, $20, $00
   Close       0,1          $00, $20, $60, $40, $C0
 
 
 The unit can be in one of several modes:
 
   - Closed
   - Select
   - Address
   - Write
   - Read
 
 I also use an 8-bit temporary value, an 8-bit address (or 7-bit address, if 128 byte EEPROM) and 9-step bit
 counter.
 
 I would assume the unit is Closed on startup (and possibly reset).
 
 
 Basic Concept overview:
 
 
   "Write 0" and "Write 1" commands advance the 9-step bit counter.  The first 8 writes fill the appropriate
 bit in the temporary value.  The 9th write will take the temp value and move it to either the address (if in
 Address mode), or to the desired area in EEPROM (if in Write mode), and the mode will update accordingly.
 Basically the first 8 writes fill the temp value and the 9th moves it to where it needs to go.
 
   Reads operate similarly... but the temp buffer isn't affected by the writes, and the 9th step doesn't copy
 the temp value anywhere.  Note however that games will perform a write between each bit read (presumably to
 advance it to the next bit) -- so you should do nothing but return the appropriate bit when the game reads
 the EEPROM I/O Reg (do not advance it to the next bit on read).
 
   "Select" mode exists on 256 byte EEPROM only (mapper 016).  It is used to select between read/write mode.
 Bit 0 of the 8-bit value written when in Select mode determines read/write mode.  On 128 byte EEPROM (mapper
 159), the high bit of the address selects read/write mode.  In both cases, 1=read mode, 0=write mode.
 
   Remember that on 128 byte, values are written low bit first... but on 256 byte, they're written high bit
 first.  Bits are read the same order they're written.
 
   Doing anything but opening when the unit is closed has no effect.
 
 
 Logic Flow Details (256-byte ... mapper 016)
 --------------------------------------------
 
 Opening from Closed Mode:
   a) Enter Select Mode
 
 Opening from non-Closed Mode:
   a) if in Select Mode, increment address by 1
   b) enter Select Mode.
   c) Reset bit counter (next write is the first write in the 9-write sequence)
 
 Writing in Select Mode:
   a) If low bit of written value = 1
      -) Enter Read Mode
   b) otherwise...
      -) Enter Address Mode
 
 Writing in Address Mode:
   a) written value becomes address
   b) Enter Write mode
 
 Writing in Write Mode:
   a) written value moves to current address of EEPROM
   b) mode is not changed
 
 Writing in Read Mode:
   a) Enter Select Mode
 
 
 
 Logic Flow Details (128-byte ... mapper 159)
 --------------------------------------------
 
 Opening from Closed Mode:
   a) Enter Address Mode
 
 Opening from non-Closed Mode:
   a) increment address by 1 (wrap $7F->00)
   b) do not change mode
   c) Reset bit counter (next write is the first write in the 9-write sequence)
 
 Writing in Address Mode:
   a) written value becomes address (low 7 bits only)
   b) if high bit of written value is set...
      -) Enter Read Mode
   c) otherwise...
      -) Enter Write Mode
 
 Writing in Write Mode:
   a) written value moves to current address of EEPROM
   b) Enter Address mode
 
 Writing in Read Mode:
   a) Enter Address Mode

See Also

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