Used by the routine at GenerateRandomNumber.

Mothership level.

Used by the routine at Handler_Pheenix_01.

The number of alien enemies "in-play" on the screen (not counting the mothership/ mothership alien which is handled separately).

Set and handled by the routine at Shield_ActivateShield.

Byte	Meaning
00	No Collision
01	Collision Detected
02	Explosion Complete

Used by the routine at Handler_ShipExplosion.

A counter that cycles from 00 to 07 controlling ship movement animation timing. Movement is skipped when the counter is 03. Also used as a timer in shield drawing routines.

Holds the mothership alien state which is used only in phase 04 to indicate if the phase has been completed or not (and then shows the bonus):

Byte	State
00	Alive
01	Dead

Used by the routine at Handler_Mothership.

Indicates whether an extra life should be awarded or not.

Maybe not directly the phase number, but when it's 04 it draws the mothership.

Indicates the start state while the title screen is showing.

Byte	Method
00	Keyboard
01	AGF joystick
02	Kempston joystick

See GameIntro.