Routines
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F54A: Step Pen Up
Used by the routines at DrawingFill and DrawingLine.
Moves the pen one pixel up the screen. E counts up from the bottom row, because PixelAddress hands it to the ROM PIXEL-ADD routine. When the pen would pass the top row (E=B0) it stays put and the zero flag is set.
StepPenUp F54A INC E Move the pen up and return when it is still on screen.
F54B LD H,A
F54C LD A,E
F54D CP $B0
F54F LD A,H
F550 RET NZ
F551 DEC E The pen passed the top row, so step back and tell the caller it did not move.
F552 XOR A
F553 LD A,H
F554 RET Return.
View the equivalent code in;
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