CPU Speed control

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Revision as of 19:08, 20 September 2020 by Ped7g (talk | contribs) (Ped7g moved page Acceleration to CPU Speed control: Acceleration is quite misleading name for this)
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Acceleration, or Turbo mode, allows the Next to run at faster clock speeds than a standard Spectrum.

Acceleration is enabled via Peripheral 2 Register ($06) and configured via CPU Speed Register ($07), or via a user control. There are three (0..2) potential settings:

  • Turbo off, or turbo on and $07 set to #00: 3.5 Mhz (standard clock).
  • Turbo on, $07 set to #01: 7 Mhz (x2). (Standard for Pentagon).
  • Turbo on, $07 set to #10: 14 Mhz. (x4) Some features, such as Layer 2 (vertically visible pixel area) and shadow-VRAM of ZX128 (whole pixel area), will automatically throttle down to 7MHz while specified areas of display are sent to the video signal.
  • Turbo on, $07 set to #11: 28 Mhz. (x8) - this mode is removed for the moment, due to HW limitations (the system was not stable enough at 28MHz).