AKAAB it's been some time since I flew A320 and in fact I don't have the FCOM's anymore I fly the A340-300 now and looking up in the FCOM's I found the following in FCOM 1 under Autoflight and Flight controls.
1.22.30 p11
SELECTED SPEED/MACH TARGET
To use a selected speed/Mach target the pilot uses the knob on the FCU to set the target speed, which is then displayed in the FCU window. It is also displayed in blue on the PFD speed scale.
Note:
The selected speed/Mach target may be set beyond VLS or VMAX, but when autothrust is active, the guidance limits the speed to VLS or VMAX.
Additionally in FCOM1 under autoflight in section 1.22.30p62
SPEED/MACH mode
In SPEED/MACH mode, the A/THR adjusts the trust in order to acquire and hold a speed or Mach target.
The Speed or Mach target may be:
- selected on the FCU by the pilot
- managed by the FMGC
When in Speed or Mach mode, the A/THR does not allow speed excursions beyond the following limits regardless of the target speed or Mach number:
- For selected speed target, the limits are VLS and VMAX (VMO-MMO, VFE-VLE, whichever applies)
- For a managed speed target, the limits are maneuvering speed (Green Dot, S, F whichever applies) and maximum speed (320/.84-VFE-VLE whichever applies)
Under FCOM 1 Flight Controls (Normal Law) 1.27.20p5
HIGH SPEED PROTECTION
The aircraft automatically recovers following a high speed upset. Depending on the flight conditions (high acceleration, low pitch attitude), the High Speed Protection is activated at/or above VMO/MMO.
When it is activated, the pitch trim wheel is frozen. Positive spiral static stability is introduced at 0deg bank angle (instead of 33 deg in normal law), so that with the sidestick released the aircraft always returns to a bank angle of 0 deg. The bank angle limit is reduced from 67 deg to 45 deg.
As the speed increases above VMO/MMO, the sidestick nose down authority is progressively reduced, and a permanent nose up order is applied to aid recovery to normal flight conditions.
The high speed protection is deactivated when the aircraft speed decreases below VMO/MMO, where the usual normal control laws are recovered. The autopilot disconnects when high speed protection goes active.
In normal law the system will keep your speed to VMO/MMO for a select speed input. In other words in cruise if you were to select MMO +0.2 lets say the A/THR would accelerate to a max speed of MMO not above not below. The same is valid for the low speed regime. If you were to select VLS -10 (with flaps extended) the A/THR would decelerate to VLS and no lower.
Hope this helps.
Regards Snails