Routines
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815B: Clear the menu screen
Used by the routines at 8039, 80FD and 812D.
Input
A Colour/attribute value (second routine only)
Two routines used in both menus - one routine to clear screen pixels, the second to clear the screen colours.
Clear the screen (pixels):
815B LD HL,$4000 Top left of screen display
815E LD DE,$1800 Number of bytes to clear
8161 LD (HL),$00 Clear screen pixels
8163 INC HL Move to next screen byte position
8164 DEC DE Decrement byte counter
8165 LD A,E
8166 OR D
8167 JR NZ,$8161 Keep clearing until counter = 0
8169 RET
Clear the screen (colours):
816A LD HL,$5800 Top left of (attribute) screen display
816D LD DE,$0300 Number of bytes
8170 LD C,A Retrieve attribute/colour value to use
8171 LD (HL),C Put colour on screen
8172 INC HL Advance to next screen square
8173 DEC DE Decrement byte counter
8174 LD A,E
8175 OR D
8176 JR NZ,$8171 Keep colouring until counter = 0
8178 RET
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