Difference between revisions of "CPU Speed control"

Revision as of 11:08, 27 January 2019

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).

@@ Line 1: / Line 1: @@
 ''Acceleration'', or ''Turbo mode'', allows the Next to run at faster clock speeds than a standard Spectrum.
-Acceleration is enabled via {{NextRegNo|$06}} and configured via {{NextRegNo|$07}}, or via a user control. There are four potential settings:
+Acceleration is enabled via {{NextRegNo|$06}} and configured via {{NextRegNo|$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 [[Reference machines|Pentagon]]).
-* Turbo on, $07 set to #10: 14 Mhz. (x4)
+* 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) Some features, such as [[Layer 2]] drawing, are disabled at this speed.
+* 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).