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/* Disadvantages */
The '''6 MHz''' CPC is a [[DIY]] hardware modification which allows to run the [[CPC6128]] with a CPU speed of 6 MHz instead of the usual 4 MHz.
== Technic ==
The 16 MHz crystal of the CPC is replaced by a 24 MHz crystal. Both crystals should kept on the main board, but a switch (a DPDT type, switching both lines to both crystals is recommended) selects between them. Keep the wiring tidy and very short. You have to select the CPU and bus speed before you switch on the CPC. Switching the speed while the system is switched on is not advised.
'''If you attempt this modification, it is at your own risk. None of the authors of this article can or will be held responsible for any damage to your CPC as a result of your DIY work.'''
== Advantages ==
* Z80 The whole computer runs with 6 MHz* 50% faster. Z80, Bus runs , RAM, CRTC run with 6 MHz, GateArray with 24MHz, Soundchip with 1.5MHz* FDC is 50% faster* , Disc formats with 50% more sectors can be usedafter adjusting the DOS paramaters* Sound that is programmed specifically for a 6MHz CPC can be sound better, since the PSG runs more quicklythan on a 4MHz CPC* Games can run more fluid
* Graphics are better, pixel are about 1/3 smaller in X
* By adjusting the CRTC an higher frame rate can be used (75 Hz)
== Disadvantages ==
* FDC Floppy disc controller also runs at 150% and can't no longer read old or write standard disc formats any longer** It is not possible to exchange discs with a 4MHz CPC.** a DOS must be used that allows to adjust disc parameters. Parados or CP/M are said to work. Unfortunately the parameters have never been documented or shared, so the values need to be figured out by anyone who tries the mod. * Not every hardware expansion is able to work with the 6 MHz bus speed. So also other options to load data and programs on a 6MHz CPC can become difficult.* Not all GateArrays will work with a 24MHz crystal* RAM should to be at least 160ns fast. Many CPCs only have 200ns RAM built-in. Replacing RAM requires to desolder the old RAM ICs.* Z80 might need being replaced by a 6MHz capable version. Pay attention to get a NMOS version of the Z80 as the CMOS version has different behavior for some undocumented but (rarely) used opcodes* Sound must be reprogrammed / patched. No patches are publicly available.
* The horizontal timing of the CRTC is affected. In order to get a stable image, you need to program register 0 at 95 (96 characters line) and Register 2 at 61 (centering for 40 characters default)
* Pixels are no longer square. Their pitch is 66.7% of their original pitch.Theses pictures show this fact (320×200 mode 1 pixels with black border)
<gallery>
Image:12062011055.JPG|Original CPC @16Mhz
Image:12062011054.JPG|Overclocked CPC @24Mhz
</gallery>
== Software ==
10 i = 0
20 after 500 goto gosub 100
25 cls
30 i = i +1
