Routines
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C37D: Advance Screen Position
Used by the routine at UpdateScreenDisplay.
Moves the screen address on by one character row (20 and 08 in the high byte).
Input
HL Screen position
Output
HL Updated screen position
AdvanceScreenPosition C37D EX DE,HL Swap in the other screen pointer, so calling this twice moves both HL and DE on by one character row.
C37E LD A,L Read the low byte of the pointer.
C37F ADD A,$20 Advance the result by 20.
C381 LD L,A Store the result in the low byte of the pointer.
C382 RET NC Return when the row still fits on the screen.
C383 LD A,H Read the high byte of the pointer.
C384 ADD A,$08 Advance the result by 08.
C386 LD H,A Store the result in the high byte of the pointer.
C387 RET Return.
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