Commodore Plus 4 - Page 276

264 Machine Language on the Commodore Plus/4
INX—Increment the X Register by 1
The value currently in the X register is incremented by 1.
Operation: X + / -* X
Addressing Mode Syntax
Flags Affected: N, Z
Opcode Bytes Cycles
Implied
INX
E8
1
The value stored in the X register is increased by 1. If the result is negative, the
N flag is set to 1; otherwise it is cleared to 0. If the result is zero, the Z flag is set to
1; otherwise it is cleared to 0.
Example: This program counts the number of times the value SEA (the opcode for a NOP)
occurs in the operating system ROM. The X register is used to count and the INX
instruction is used to update it.
. 2000
. 2002
. 2004
. 2005
. 2006
. 2008
. 200A
. 200C
. 200E
. 2010
. 2011
. 2013
. 2015
. 2017
. 2019
A9
85
AA
A8
A9
85
Bl
C9
DO
E8
E6
DO
E6
DO
00
00
D8
80
D9
D8
EA
01
D8
P5
D9
PI
LDA
STA
TAX
TAY
LDA
STA
LDA
CMP
BNE
INX
INC
BNE
INC
BNE
BRK
#$oo
$D8
#$80
$D9
($D8),Y
#$EA
$2011
$D8
$200A
$D9
$200A
Load .A with zero.
Store zero in the low byte of the
address.
Store zero in .X, the count register.
Store zero in .Y, the index register.
Load .A with $80.
Store $80 in the high byte of the
address.
Get the value at the current address.
Compare with $EA.
If not equal, go on.
Increment the count register.
Increment the low byte of the
address.
If not zero, go back for the next byte
Increment the high byte of the
address.
If not zero, go back for the next byte
Stop processing.
When the BRK instruction is executed, the count in the X register is displayed.