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).
Mirroring is hard-wired to Horizontal.
Mask: $F800
A~FEDC BA98 7654 3210
-------------------
0100 1... ..A. BC..
+--++--- Latch value
+--- IRQ control
Power-on value (ABC): $7
If counting is enabled, the counter is clocked on every falling edge of M2. IRQ is asserted while ((counter÷640)&37)=37, so it is asserted the first time when the counter reaches 23680 and self-acknowledges the first time when it reaches 24320.
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.
Categories: FDS conversion mappers, Mappers with CHR RAM, Mappers with fixed-timing cycle IRQs