Routines
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0E9B: THE 'CL-ADDR' SUBROUTINE
Used by the routines at PO_SCR, CL_SET, CL_SC_ALL and CL_LINE.
For a given line number, in the B register, the appropriate display file address is formed in the HL register pair.
Input
B Line number
Output
HL Display file address
CL_ADDR 0E9B LD A,$18 The line number has to be reversed.
0E9D SUB B
0E9E LD D,A The result is saved in D.
0E9F RRCA In effect '(A mod 8)*32'. In a 'third' of the display the low byte for the first line is +00, for the second line +20, etc.
0EA0 RRCA
0EA1 RRCA
0EA2 AND $E0
0EA4 LD L,A The low byte goes into L.
0EA5 LD A,D The true line number is fetched.
0EA6 AND $18 In effect '64+8*INT (A/8)'. For the upper 'third' of the display the high byte is +40, for the middle 'third' +48, and for the lower 'third' +50.
0EA8 OR $40
0EAA LD H,A The high byte goes to H.
0EAB RET Finished.
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