Commodore Plus 4 - Page 267

The 6502 Microprocessor 235
. 2001 A9 OD LDA #$0D Get the low byte of the address of the
new IRQ processor.
. 2003 8D 14 03 STA $0314 Store in the vector.
. 2006 A9 20 LDA #$20 Get the high byte of the address of
the new IRQ processor.
. 2008 8D 15 03 STA $0315 Store in the vector.
. 200B 58 CLI Reenable the interrupts.
. 200C 00 BRK Stop processing.
. 200D EE 19 PP INC $PF19 Increment the border color.
. 2010 40 OE CE JMP $CE0E Jump to normal IRQ processing.
After you execute this program (by typing G 2000), the processing of an
interrupt increments the border color before proceeding normally. When you are
finished with this example, reset the computer by typing G FFF6 so as to restore
the IRQ vector to its default value.
CLV—Clear Overflow Flag
The overflow flag is cleared to 0.
Operation: 0 — V Flags Affected: V
Addressing Mode Syntax Opcode Bytes Cycles
Implied CLV B8 1 2
Example: This program uses the overflow flag to perform an unconditional branch. Such a
branch may be used instead of a jump instruction when code must be relocatable.
sooo
S001
2003
2004
2007
B8
50
00
EE
00
01
19
CLV
BVC
BRK
PF IUC
BRK
$2004
j$FF19
Clear the overflow flag.
This branch is always taken.
This is never executed.
Increment the border color.
Stop processing.
Unless a JMP or branch instruction elsewhere starts processing at $2001, the
branch there is unconditional (always taken).
CMP—CMP Memory with. Accumulator
The value currently in the accumulator is compared with the specified operand
and the appropriate flags are set.