NES 2.0 Mapper 545
NES 2.0 Mapper 545 denotes the ST-80 PCB, used by the 壽石組合 4-in-1 Super Combo 1216k multicart. It contains three 128K PRG-ROM+128K CHR-ROM TLROM games, plus one 256K+128K one (Super Mario Bros. 3). It mounts two PRG-ROM chips, a 512 KiB one, and a 128 KiB one. The first, 512 KiB, one contains the PRG-ROM data for the first three games that have 128 KiB of PRG-ROM per game, plus the second 128 KiB half of the game that has 256 KiB of PRG-ROM. The second, 128 KiB, PRG-ROM chip contains the first 128 KiB half of the game that has 256 KiB of PRG-ROM. The .NES file contains the 512 KiB of PRG-ROM of the first chip, followed by the 128 KiB of the second chip, for a total of 640 KiB of PRG-ROM.
D~[.... DCBA] A~[1111 ...1 ..1. ....] (Address & $F120)==$F120
||++- PRG/CHR A18..A17 within first ROM chip
++--- 0: force CHR A16 high
| 1: normal CHR A16 mode
+---- 0: 128 KiB PRG mode
1: 256 KiB PRG mode: Use second ROM chip if MMC3 A17=0
Power-on value: $00
The “force CHR A16 high” business is only used during the menu.