Routines
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51483: Read Interface 2 Joystick
Reads the controls from the Interface 2 joysticks, which are the keys 1 to 5 for the first joystick and 6 to 0 for the second joystick. The joysticks use the keys left, right, down, up and fire in that order, so the keys of the first joystick are reversed to put them in the same order as the keys of the second joystick.
Output
C The controls
Reverse the keys 1 to 5.
ReadInterface2Joystick 51483 LD A,247 Read from the keyboard;
Port Number Bit
0 1 2 3 4
247 1 2 3 4 5
51485 CALL ReadKeyboardPort
51488 PUSH BC Stash BC on the stack.
51489 LD B,5 Set B to 5.
ReadInterface2Joystick_Reverse 51491 RRA Rotate A right.
51492 RL C Rotate C left.
51494 DJNZ ReadInterface2Joystick_Reverse Jump to ReadInterface2Joystick_Reverse until B is zero.
51496 LD A,C Copy C to A.
51497 POP BC Restore BC from the stack.
51498 LD C,A Copy it to C.
Merge the keys 6 to 0.
51499 LD A,239 Read from the keyboard;
Port Number Bit
0 1 2 3 4
239 0 9 8 7 6
51501 CALL ReadKeyboardPort
51504 OR C Merge C.
51505 LD C,0 Set C to 0.
51507 BIT 0,A Set bit 3 of C if bit 0 of A is set.
51509 JR Z,ReadInterface2Joystick_TestUp
51511 SET 3,C
ReadInterface2Joystick_TestUp 51513 BIT 1,A Set bit 2 of C if bit 1 of A is set.
51515 JR Z,ReadInterface2Joystick_TestDown
51517 SET 2,C
ReadInterface2Joystick_TestDown 51519 BIT 2,A Set bit 4 of C if bit 2 of A is set.
51521 JR Z,ReadInterface2Joystick_TestRight
51523 SET 4,C
ReadInterface2Joystick_TestRight 51525 BIT 3,A Set bit 1 of C if bit 3 of A is set.
51527 JR Z,ReadInterface2Joystick_TestLeft
51529 SET 1,C
ReadInterface2Joystick_TestLeft 51531 BIT 4,A Set bit 0 of C if bit 4 of A is set.
51533 JR Z,ReadInterface2Joystick_Finish
51535 SET 0,C
ReadInterface2Joystick_Finish 51537 JP ReadControls_Finish Jump to ReadControls_Finish.
View the equivalent code in;
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