Port Expander IC24 (Sega Mega-Tech) Updated Mar 15, 2026 · 14 min read · Support · 0 viewing 🔥 Most active page right now Log in or register to read the full article. Previous Button Interface (Sega Mega-Tech) The IC24 I/O Expander connects the SMS Z80 data pins through to the CN2 (Select Buttons) and CN4 (Pl... Next Test Mode (Sega Mega-Tech) Test mode can be entered only when there is at least one valid game in the slot, otherwise pressing ...