Commodore Plus 4 - Page 281

The 6502 Microprocessor 869
. 2000 A2 27 LDX #$27 Initialize .X for indexing.
. 2002 BD 00 OC LDA $0C00,X Get the next character.
. 2005 9D 01 OC STA #0C01,X Store 1 byte to the right.
. 2008 CA DEX Decrement the index register.
. 2009 10 F7 BPL $2002 If not done, go back.
. 200B 00 BRK Stop processing.
If the screen scrolls upon execution of the BRK instruction, the effect of the
program will not be seen. To avoid this, clear the screen before executing the
program.
LDY—Load Y Register with Value from Memory
The value currently in the location specified by the operand is placed in the Y
register.
Operation: M-+ Y Flags Affected: N, Z
Addressing Mode Syntax Opcode Bytes Cycles
Immediate
Zero page
Zero page,X
Absolute
Absolute, X
LDY #$hh
LDY $hh
LDY $hh,X
LDY $hhhh
LDY $hhhh,X
AO
A4
B4
AC
BC
2
2
2
3
3
2
3
4
4
4*
* Add 1 when a page boundary is crossed.
If the value transferred is negative, the N flag is set to 1; otherwise it is cleared to
0. If the value transferred is zero, the Z flag is set to 1; otherwise it is cleared to 0.
The value in the operand is not altered.
Example: This program copies the characters on the first line of the screen to the second.
The Y register is used as the index and initialized with the LDY instruction.
. 2000 A9 OC LDA #$0C Load .A with the high byte of the
address.
. 2002 85 D9 STA $D9 Store in the high byte of the
originating address.
. 2004 85 DB STA $DB Store in the high byte of the
destination address.
. 2006 A9 00 LDA #$00 Load .A with the low byte of the first
line address.