Commodore Plus 4 - Page 280

368 Machine Language on the Commodore Plus/4
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: The characters on the top of the line of the screen are copied to the second line of
the screen. Each value is transferred by loading it into the accumulator with the
LDA instruction and storing it to the destination.
. 2000 AS 27 LDX #$27 .X indexes the line.
. 2002 BD 00 OC LDA $0C00,X Load the accumulator with the next
character.
. 2005 9D 28 OC STA $0C28,X Store on the second line.
. 2008 CA DEX Decrement the index register.
. 2009 10 F7 BPL $2002 If there is more to do, go back.
. 200B 00 BRK Stop processing.
If the BRK instruction causes the screen to scroll, the result of the program is
not seen. To avoid this, clear the screen before you execute the program.
LDX—Load X Register with Value from Memory
The value currently in the location specified by the operand is placed in the X
register.
Operation: M— X Flags Affected: N, Z
Addressing Mode Syntax Opcode Bytes Cycles
Immediate
Zero page
Zero page, Y
Absolute
Absolute, Y
LDX #$hh
LDX $hh
LDX $hh,Y
LDX $hhhh
LDX $hhhh,Y
A2
A6
B6
AE
BE
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 each character on the first line of the screen one location to
the right. The X register is used as the index and initialized using the LDX
instruction.