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C't 512 KB internal RAM expansion

164 bytes added, 15:03, 8 May 2010
* The bank selection for CPU address 4000h..7FFFh does also affect bank bits0-1 for VRAM at 4000h..7FFFh; thus the CRTC may see bank 0-3 in that region (whilst, as far as known, on a normal CPC, it should always see bank 1 in that region).
** '''Notice''' the included sample program '''does''' seem to map VRAM to 4000h, whilst mapping expansion banks to 4000h at the same time. Theoretically, this should result in display glitches - unknown if/how/why the sample works [?]
* The expansion seems to have been designed independently of [[Standard Memory Expansions]] like the dk'tronics one. So, there is no (intended) compatibility. However, both c't and dk'tronics are designed around the CPC6128 banking mechanism, so they do work similar in some ways. Namely, both can map expansion banks to 4000h..7FFFh, but there are several differences:
** For the mapping to 4000h..7FFFh, dk'tronics uses values CCh..CFh, D4h..C7h, DCh..DFh, ... FCh..FFh whilst c't uses values C8h..DFh. Some of these values do overlap, providing some (unintended) semi-compatibility, but there's still one big differences: along with the above values, dk'tronics maps bank 3 to C000h..FFFFh, whilst c't maps bank 7 to that region.
== Memory Configurations ==
* The "*" and "+" operators are meaning "* = AND", "+ = OR". The idea behind that confusing syntax was to make it "easier" to learn for people who are trained only in basic maths (the formulas do also work when treating *=multiply, and +=plus. For example: 1+0+1+1 = 3 = nonzero = true).
* There must be some priority ordering in the formulas: Either * before +, or operations inside of a line before merging the results of the separate lines (in above examples, both ordering methods do work).
 
== Newer Info ==
 
Having a short look at the article, it seems to be all different as than expected:
 
* There is no dk'tronics compatibility intended - however, c't and dk'tronics are based on the CPC6128 banking mechanism, so they work similar, and to some level there is some (unintended) compatibility. Namely, ONE HALF of the memory can be accessed in dk'tronics style fashion.
 
* There seems to be no hardware based "Video RAM" support at all. However, there's some unspectacular software based example included that copies expansion RAM to VRAM via LDIR opcode.
== Scanned Article / Schematics ==
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