How in the hell did you get a game running off the expansion port? And with a memory mapper no less.
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The expansion port includes all Hu-Card connectors, so games can also be launched through the expansion port. SF2 is the only PC-Engine game that uses a MAPPER. To accommodate the MAPPER and to facilitate the procurement of ROM & MAPPER ICs, a large cartridge design was adopted. However, optimizing it for Hu-Card is not difficult and can be done later when there is time.