jetpac: Routine at 735e

735e: Check if thrust (up) button is pressed.

Used by the routines at 7412 and 753c.

Output
A	thrust button, $FE = pressed, $FF = no input - like joystick: 000LRDUF.

735e

ld a,($5cf3)

Game options

7361

bit 1,a

Use Joystick?

7363

jr nz,$7302

Jump if so

7365

ld b,$02

Loop count: read left and right row of keys

7367

ld a,$fb

Row: Q,W,E,R,T

7369

out ($fd),a

Set port for reading keyboard

736b

in a,($fe)

...and read that row of keys

736d

and $1f

736f

cp $1f

Check if any keys on the row are pressed

7371

jr nz,$737a

Jump if so - key press detected

7373

ld a,$df

Row: Y,U,I,O,P

7375

djnz $7369

Loop back and read input again

7377

ld a,$ff

Still no input detected

7379

ret

737a

ld a,$fd

A=UP (thrust) : 1111 1101

737c

ret