Routines
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C41F: Get Keypress
Used by the routines at GameEntryPoint, A4CD and WaitForKeypress_Loop.
Output
A Keypress value, or 00 for no keypress
GetKeypress C41F PUSH IY Stash IY, IX, HL, DE and BC on the stack.
C421 PUSH IX
C423 PUSH HL
C424 PUSH DE
C425 PUSH BC
C426 LD IY,$5C3A IY=ERR_NR.
C42A EI Enable interrupts.
C42B HALT Halt operation (suspend CPU until the next interrupt).
C42C DI Disable interrupts.
C42D LD A,($5C3B) Jump to GetKeypress_Process if bit 5 of *FLAGS is set, indicating that a key has been pressed.
C430 BIT 5,A
C432 JR NZ,GetKeypress_Process
No key has been pressed.
C434 XOR A Load A with 00 (no keypress).
C435 JR GetKeypress_Return Jump to GetKeypress_Return.
A key has been pressed, so process it.
GetKeypress_Process C437 RES 5,A Reset bit 5 of *FLAGS which resets "when a new key has been pressed".
C439 LD ($5C3B),A
C43C LD A,($5C08) Jump to GetKeypress_CheckDelete if *LAST-K (last key pressed) is not ASCII 5F ("_").
C43F CP $5F
C441 JR NZ,GetKeypress_CheckDelete
C443 LD A,$18 A=18.
Did the player press "DELETE"?
GetKeypress_CheckDelete C445 CP $0C Jump to GetKeypress_CheckUp if *LAST-K (last key pressed) is not ASCII 0C ("DELETE").
C447 JR NZ,GetKeypress_CheckUp
C449 LD A,$08 Load A with 08 (delete was pressed).
Did the player press "UP"?
GetKeypress_CheckUp C44B CP $0B Jump to GetKeypress_Validate if *LAST-K (last key pressed) is not ASCII 0B ("UP").
C44D JR NZ,GetKeypress_Validate
C44F LD A,$5B Load A with 5B (up was pressed).
GetKeypress_Validate C451 CALL ValidateKeypress Call ValidateKeypress.
C454 SET 7,A Set bit 7 of A.
GetKeypress_Return C456 POP BC Restore BC, DE, HL, IX and IY from the stack.
C457 POP DE
C458 POP HL
C459 POP IX
C45B POP IY
C45D RET Return.
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