BattleCity [Model DMG-BCA]

Stage select:
At the Stage number screen, press Up or Down to choose a level up to 32 by default. When you beat any games above, you'll be able to select it as well. Beat the game to unlock all levels.
Source: gamefaqs.com

Cheat sequences:
All cheats are entered at the title screen. A sound will confirm correct code entry. Any number of cheats may be entered, all effects are combined.
Left, Left, B, A, Up, Down, A, Right - Start with 9 lives.
Down, Up, Up, Down, Left, Right, A, B - Unlock all stages in Stage select mode.
B, A, B, B, A, B, A, A - Start with level 3 tank.
Down, Left, Up, A, Right, Right, B, Up - Options menu. Allows you to select game speed, lives and extend mode, which determines one of two score tables for obtaining a new life.
Right, Up, A, Down, B, Left, A, B - Increase number of enemies after Stage 5 on the field at the same time up to 6 (default is 4).
Up, Up, Down, Up, Left, Right, Right, Left - Shovel power-up will use a random block.
Up, B, Left, A, Right, B, Down, A - Enables an auto-fire.
A, Down, A, Up, A, Right, B, Left - Credits, but without unlocking all stages.