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mg_notes:iie_card:gemini_vs_megaii [2019/08/26 03:56] (current) M.G. created |
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+ | ====== 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: | ||
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+ | ^ 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 | |