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20709: Populate a row of the screen with machine code
Used by the routine at 33204. Copies 256 bytes of machine code from the source (either the top row of the screen, or character buffers 183-190) to the destination (the second or third row from the bottom of the screen), in eight 32-byte blocks.
HL Source (16384 or 46848)
DE Destination display file address (20640 or 20672)
20709 LD BC,32 There are 32 bytes per row of pixels
20712 PUSH DE
20713 LDIR Copy 32 bytes to the display file
20715 LD L,B L=0
20716 POP DE
20717 INC D Point DE at the start of the next row of pixels
20718 INC H Point HL at the next batch of 32 bytes to copy
20719 BIT 3,D Have we copied 8 rows of bytes yet?
20721 JR Z,20709 Jump back if not
20723 RET
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