Changes
== 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 (2 lines at leasta DPDT type, better 3switching 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 is can or will be held responsible for danger on any damage to your CPC, in case you try to use this as a result of your DIYwork.
== Advantages ==
* A lot of games run well with 6 MHz. For example: Nebulus, StarFox, Starstrike and others.
* There is a 6 MHz version of FutureOS
== Testing ==
* Your CPC may work with the higher speed crystal if the rest of the system hardware is able to operate at this speed. You are more likely to be successful if the DRAM chips fitted to your machine are the higher speed versions (lower access time). Please refer to the relevant DRAM data sheet for details of the access time and on the type numbers and markings on the DRAM chips.
*If any part of the hardware system is unable to properly function at the higher speed, likely symptoms of the hardware not being happy are failure to properly initialise to the start up screen. Or symptoms similar to a RAM fault.
* This modification has been successful on some CPCs (manufactured with fast DRAMs) and verified with at least one CPC6128 produced in 1987.
== Measurement of speed ==
* The CPU will operate at an increased speed proportional to the increased frequency of the crystal.
* With a 24 MHz crystal, the 4 MHz clock (CPU speed) should be 6 MHz. This is a 50% speed increase.
* Some CPCs (manufactured with fast DRAMs) show a increase of speed by 50% (verified with at least one CPC6128 produced 1987). * In case of If your machine starts up okay, you can test the older DRAM type the speed improvement is only 16.7%.This has been tested modification with this simple program :
10 i = 0
100 end
Score is 258 on normal CPC versus 301 on when using a CPC fitted with a 24 MHz CPCcrystal.
(Theses results can be subject to discussion as we are not sure interrupts how interrupt timing is not affected).
[[Category:DIY]][[Category:Hardware]]
