Routines
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0E88: THE 'CL-ATTR' SUBROUTINE
Used by the routines at CL_SC_ALL and CL_LINE.
This subroutine has two separate functions.
  • For a given display area address the appropriate attribute address is returned in the DE register pair. Note that the value on entry points to the 'ninth' line of a character.
  • For a given line number, in the B register, the number of character areas in the display from the start of that line onwards is returned in the BC register pair.
Input
B Line number
C +00
HL Display file address
Output
BC Number of spaces from the given line number (B) downwards
DE Corresponding attribute file address
CL_ATTR 0E88 LD A,H Fetch the high byte.
0E89 RRCA Multiply this value by thirty two.
0E8A RRCA
0E8B RRCA
0E8C DEC A Go back to the 'eight' line.
0E8D OR $50 Address the attribute area.
0E8F LD H,A Restore to the high byte and transfer the address to DE.
0E90 EX DE,HL
0E91 LD H,C This is always zero.
0E92 LD L,B The line number.
0E93 ADD HL,HL Multiply by thirty two.
0E94 ADD HL,HL
0E95 ADD HL,HL
0E96 ADD HL,HL
0E97 ADD HL,HL
0E98 LD B,H Move the result to the BC register pair before returning.
0E99 LD C,L
0E9A RET
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