Commodore Plus 4 - Page 262

280 Machine Language on the Commodore Plus/4
BNE—Branch If Zero Flag Is Clear
This instruction examines the current status of the zero flag bit. If it is cleared to 0,
the branch occurs. If it is 1, the branch does not occur, and execution continues
with the following instruction.
Operation: Branch onZ-0 Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Relative BNE $hhhh DO 2 2*
* Add 1 cycle when the branch is taken. Add 2 cycles when it is taken across a page boundary.
Example: In this program, the contents of $2100-$21FF are copied into $2200-$22FF. The
BNE instruction is used to continue looping until the X register reaches zero.
. 2000 A2 00 LDX #$00 Start counter at zero.
. 2002 BD 00 21 LDA $2100,X Get value from original area.
. 2005 9D 00 22 STA $2200,X Put value in destination area.
. 2008 CA DEX Decrement counter.
. 2009 DO P7 BWE $2002 If not done, go back.
• 200B 00 BRK Stop processing.
Use the M (Memory) command to examine or change the contents of the
memory areas.
BPL—Branch If Negative Mag Is Clear
This instruction examines the current status of the negative flag bit. If it is cleared
to 0, the branch occurs. If it is 1, the branch does not occur, and execution
continues with the following instruction.
Operation: Branch onN-0 Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Relative BPL $hhhh 10 2 2*
* Add 1 cycle when the branch is taken. Add 2 cycles when it is taken across a page boundary.
Example: This program copies the contents of the color registers ($FF15-$FF19) into
memory at $2100-$2104. The BPL instruction is used to determine when the
process is complete.