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50E5: Populate a row of the screen with machine code
Used by the routine at 81B4. Copies 256 bytes of machine code from the source (either the top row of the screen, or character buffers 0xB7-0xBE) to the destination (the second or third row from the bottom of the screen), in eight 32-byte blocks.
HL Source (4000 or B700)
DE Destination display file address (50A0 or 50C0)
50E5 LD BC,$0020 There are 32 bytes per row of pixels
50E9 LDIR Copy 32 bytes to the display file
50EB LD L,B L=0x00
50ED INC D Point DE at the start of the next row of pixels
50EE INC H Point HL at the next batch of 32 bytes to copy
50EF BIT 3,D Have we copied 8 rows of bytes yet?
50F1 JR Z,$50E5 Jump back if not
50F3 RET
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