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Post by RichardC64 on Dec 3, 2014 16:27:04 GMT
If the upper nybble were made available, then when 80 columns was in use there'd be 2K available (in 1K "banks") as out-of-the-way memory for whatever purpose. www.sdiy.org/richardc64/color/byte.html (Instruction are for the low-profile '128.) Q:Do I have to register here all over again? Login is unable to find any of my email addresses I tried logging in with.
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Post by hydrophilic on Dec 4, 2014 5:36:13 GMT
Yeah it is strange that full (8-bit-wide) RAM chip was used but only the low 4-bits are connected. Surely this was for C64 compatibility, because they had to actually add 4 resistors to stabilize the unused bits! Those four resistors were just a few cents, but when you multiply that by millions of units, that is tens of thousands of dollars that CBM 'invested'... or as some may say 'wasted'. Umm, actually they didn't waste the money, they passed the cost to the consumer But if you like hardware hacking, then it is a great 'benefit'... now you have cool (and useful!) project. Thanks for the link! After reading the article (wow, 1990) it seems that 4 resistors was much cheaper than another 4066 chip! Has anybody built this? Any software to demonstrate the amazing power of an extra 2K ?
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richardc64
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Posts: 5
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Post by richardc64 on Dec 4, 2014 12:36:01 GMT
Yeah it is strange that full (8-bit-wide) RAM chip was used but only the low 4-bits are connected. Surely this was for C64 compatibility, because they had to actually add 4 resistors to stabilize the unused bits! Those four resistors were just a few cents, but when you multiply that by millions of units, that is tens of thousands of dollars that CBM 'invested'... or as some may say 'wasted'. Umm, actually they didn't waste the money, they passed the cost to the consumer I think wasting half a 2Kx8 RAM was the most cost-effective way to provide two color banks. It's a shame the VIC wasn't made to utilize the upper 4 bits, but that probably would've created problems in 64 mode. I'm probably the only person who ever did this mod. I only used the extra memory (when in 80 columns) as an "alternative" common memory to do bank switching when normal common memory wasn't present.
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Post by mirkosoft on Dec 4, 2014 16:12:08 GMT
Nice!
Nice mod! I told always that 64 compatibility was wrong step of Commodore... I take look at if I'll be able to do it!
Miro
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