NES 2.0 Mapper 548

NES 2.0 Mapper 548 denotes 科統實業股份有限公司 (Co Tung Co.)'s CTC-15 circuit board, used for their cartridge conversion of the FDS game Almanaの奇跡 (Almana no Kiseki).

Banks

• CPU $6000-$7FFF: 8 KiB unbanked PRG-RAM
• CPU $8000-$BFFF: Switchable 16 KiB PRG-ROM bank
• CPU $C000-$FFFF: Fixed 16 KiB PRG-ROM bank #3
• PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM

Mirroring is hard-wired to Horizontal.

Registers

Latch and IRQ control ($4800, write)

Mask: $F800

A~FEDC BA98 7654 3210
  -------------------
  0100 1... ..A. BC..
              +--++--- Latch value
                  +--- IRQ control

Power-on value (ABC): $7

• The latch value is not used until the Latch Apply register is writtent o.
• IRQ control:
  • 0: Enable M2 counting and IRQ generation
  • 1: Disable M2 counting and IRQ generation, acknowledge IRQ.

If counting is enabled, the counter is clocked on every falling edge of M2. An IRQ is generated at a counter value of 23680 and self-acknowledged at a value of 24320.

Latch Apply ($5000, write)

Mask: $F800

Upon writing to the $5000-$57FF address range, the latched value written to $4800 is XOR'd with $05 and applied as the 16 KiB PRG-ROM bank at CPU $8000-$BFFF. The power-on bank is $7.

See also

PCB image and analysis