Hex cheats:

The saved games data are in the files STATEx.DAT where x is 1 thru 5 and represent the five save game slots in the game.

Hex address 4EE5 contains the amount of player energy. Hex 00 is max.
Hex address 4B7C contains the number of shots for weapon 1.
Hex address 4B7D contains the number of shots for weapon 2.
Hex address 4B7E contains the number of shots for weapon 3.
Hex address 4B7F contains the number of shots for weapon 4.
Hex address 4B80 contains the number of shots for weapon 5 (reset to 00 at beginning of every new level).

99 shots is the max amount the game allows for the weapons, so hex 63 thru hex FF will all result in 99 shots, but hex 63 should be used because if more of the ammo for a weapon is picked up, it still adds to the value. So for example, if hex FF is used and ammo is picked up, the value will wrap around to 00 and then up from there. Hex address 4B8B contains the number of shots for the robot's weapon. Unlike the regular weapons, this one seems to give the number of shots for whatever value is entered there. Still, hex FF or values near hex FF should not be used.

Hex address 4F22 begins the codes for the inventory items. Every other byte contains a code for an inventory item and continues until the hex value at address 4FEA has been reached. So, if there is a hex 04 at address 4FEA, then address 4F22, 4F24, 4F26, and 4F28 will be
enabled.

The following list shows the codes:

Hex 01 = Silver Key
Hex 02 = Heart (replenishes energy)
Hex 03 = N/A
Hex 04 = Robot
Hex 05 = Gold Key
Hex 06 = Bomb (kills all enemies on screen)
Hex 07 = Lightning stopper
Hex 08 = Robot ammo (2 shots)

The maximum number of inventory items is 100 (hex 64), but since the game adds picked up items at the end and scrolling thru the items doesn't wrap around from 1 to 100, it would take a long time to find the new items to use