Routines
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50045: Advance Screen Position
Used by the routine at UpdateScreenDisplay.
Moves the screen address on by one character row (32 and 8 in the high byte).
Input
HL Screen position
Output
HL Updated screen position
AdvanceScreenPosition 50045 EX DE,HL Swap in the other screen pointer, so calling this twice moves both HL and DE on by one character row.
50046 LD A,L Read the low byte of the pointer.
50047 ADD A,32 Advance the result by 32.
50049 LD L,A Store the result in the low byte of the pointer.
50050 RET NC Return when the row still fits on the screen.
50051 LD A,H Read the high byte of the pointer.
50052 ADD A,8 Advance the result by 8.
50054 LD H,A Store the result in the high byte of the pointer.
50055 RET Return.
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