INES Mapper 015

The iNES format assigns iNES Mapper 015 as the mapper used in 100-in-1 Contra Function 16, the first pirate multicart to be emulated.

The mapper allows multiple NROM or BNROM games plus one UNROM game to be used with very little modification. A few games originally released on a CNROM compatible board (such as two variants of Tetris) showed up on the cart; these were ripped to NROM by tossing out all 8 KB CHR banks except the one used for gameplay.

Overview

• PRG ROM size: Up to 512 KB
• PRG ROM bank size: 8 KB, 16 KB, or 32 KB
• PRG RAM: 8 KB
• CHR capacity: 8 KB RAM
• CHR bank size: None
• Nametable mirroring: Controlled by mapper
• Subject to bus conflicts: Unknown

Banks

There is one switchable bank. How this is mapped into depends on the current bank mode (see Registers below).

Bank mode 0 ( 32K )

• CPU $8000-$BFFF: Bank B
• CPU $C000-$FFFF: Bank (B OR 1)

If bit 0 of B equals 1, then bank modes 1 and 2 are identical.

Bank mode 1 ( 128K )

• CPU $8000-$BFFF: Switchable 16 KB bank B
• CPU $C000-$DFFF: Fixed to last bank in the cart

This mode uses the same configuration as UNROM.

Bank mode 2 ( 8K )

• CPU $8000-$9FFF: Sub-bank b of 16 KB PRG ROM bank B
• CPU $A000-$FFFF: Mirrors of $8000-$9FFF

Bank mode 3 ( 16K )

• CPU $8000-$BFFF: 16 KB bank B
• CPU $C000-$FFFF: Mirror of $8000-$BFFF

Registers

Control ($8000-$FFFF)

This is a 10-bit register. The upper 2 bits of the value are set from address lines A1-A0.

15 bit  8 7  bit  0  Address bus
---- ---- ---- ----
1xxx xxxx xxxx xxSS
|                ||
|                ++- Select PRG ROM bank mode
|                    0: 32K; 1: 128K (UNROM style); 2: 8K; 3: 16K
+------------------- Always 1

7  bit  0  Data bus
---- ----
bMBB BBBB
|||| ||||
||++-++++- Select 16 KB PRG ROM bank
|+-------- Select nametable mirroring mode (0=vertical; 1=horizontal)
+--------- Select 8 KB half of 16 KB PRG ROM bank
           (should be 0 except in bank mode 0)

The result when b=1 outside of bank mode 0 is not specified.

Power-up state: bank mode 2, bank 0, mirroring not specified.

Variants

 Here are Disch's original notes:
 ========================
 =  Mapper 015          =
 ========================
 
 Example Game:
 --------------------------
 100-in-1 Contra Function 16
 
 
 Notes:
 ---------------------------
 
 Possible bus conflicts???
 
 
 
 Registers:
 ---------------------------
 
   $8000-FFFF:  A~[.... .... .... ..OO]
                  [pMPP PPPP]
     O = Mode
     p = Low bit of PRG page (not always used)
     P = High bits of PRG page
     M = Mirroring  (0=Vert, 1=Horz)
 
 
 PRG Setup:
 ---------------------------
 
 Depending on the Mode used, the 'p' bit may not be used.  In the chart below, "P" will indicate that only the
 'P' bits are used to form a 6-bit page number... whereas "Pp" will indicate the full 7-bit page number.
 
 
            $8000   $A000   $C000   $E000  
          +---------------+---------------+
 Mode 0:  |       P       |     P OR 1    |
          +---------------+---------------+
 Mode 1:  |       P       |     { -1}     |
          +---------------+---------------+
 Mode 2:  |  Pp   |  Pp   |  Pp   |  Pp   |
          +---------------+---------------+
 Mode 3:  |       P       |       P       |
          +---------------+---------------+
 
 
 Powerup:
 ---------------------------
 All regs reset to 0 on powerup.