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E8A1: test for line decrement
Used by the routine at E716.
E8A1 A2 02 LDX #$02 set the count
E8A3 A9 00 LDA #$00 set the column
E8A5 C5 D3 CMP $D3 compare the column with the cursor column
E8A7 F0 07 BEQ $E8B0 if at the start of the line go decrement the cursor row and exit
E8A9 18 CLC else clear carry for add
E8AA 69 28 ADC #$28 increment to next line
E8AC CA DEX decrement loop count
E8AD D0 F6 BNE $E8A5 loop if more to test
E8AF 60 RTS
E8B0 C6 D6 DEC $D6 else decrement the cursor row
E8B2 60 RTS
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