# Differences

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 — ​mg_notes:iie_card:gemini_vs_megaii [2019/08/26 03:56] (current)M.G. created 2019/08/26 03:56 M.G. created 2019/08/26 03:56 M.G. created Line 1: Line 1: + ====== Gemini vs Mega II ====== + The Gemini chip of the Apple %%//%%e Card is often compared to the Mega II chip of the Apple IIgs.  The descriptions often vary from "newer version of" or "​slightly revised"​ when comparing the the two.  I believe these statements to be incorrect, and will attempt to demonstrate such via a direct comparison: + + ^ Criteria ^ Mega II ^ Gemini ^ References and Notes ^ + | Pin Count | 84 | 128 | + | Busses | ADBUS \\ MDBUS \\ '816 Address Bus (low 16 bits) \\ SBUS | PDS Address \\ PDS Data \\ 6502 Address \\ 6502 Data | http://​www.classiccmp.org/​cini/​pdf/​Apple/​Apple%20IIgs%20schematic.pdf \\ SBUS -> Slotmaker on IIgs | + | CPU Control | No | Yes | On IIgs, these are generated by the FPI. | + | DRAM bus width | 8 bits | 9 bits | | + | Video Circuit | Yes | No | See IIgs Schematic, above. | + | Floating Bus | Yes | No | | + | Slot bus signals | Yes | No | Gemini only supports real I/O for an IWM in "​slot"​ 6. | + | 3.5DRIVE and HDSEL | No | Yes | VGC handles these on IIgs. | + | Mouse Interface | Yes | No | | + | Traps/CPU Pause | No | Yes | http://​www.1000bit.it/​support/​manuali/​apple/​technotes/​aiie/​tn.aiie.10.html |