Commodore Plus 4 - Page 295

The 6802 Microprocessor 283
STX—Store Value in X Register into Memory
The value currently in the X register is placed in the location specified by the
operand.
Operation: X - M Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Zero page STX $hh 86 2 3
Zero page, Y STX $hh,Y 96 2 4
Absolute STX $hhhh 8E 3 4
The value of the X register is not altered, and the flags are not altered.
Example: This program counts the number of locations containing the value SEA (the
opcode for a NOP) in $D A00-$DAFF. The X register is used as the counter, and
the final count is stored in $2100 using the STX instruction.
. S000 AS 00 LDX #$00 Start .X count at zero.
. 2002 AO 00 LDY #$00 .Y is the index register.
. 2004 A9 EA LDA #$EA Load .A with the value to look for.
. 2006 D9 00 DA CMP $DA00,Y Check the next byte.
2009
200B
200C
200D
200F
2012
DO
E8
88
DO
8E
00
01
F7
00 21
BITE
IWX
DEY
BNE
STX
BRK
$2000
$2006
#2100
If not equal, then skip the next
instruction.
Increment the count.
Decrement the index register.
If not done, go back.
Store the final count at $2100.
Stop processing.
STY—Store Value in Y Register into Memory
The value currently in the Y register is placed in the location specified by the
operand.
Operation: Y'-+ M Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Zero page STY $hh 84 2 3
Zero page, X STY $hh,X 94 2 4
Absolute STY $hhhh 8C 3 4
The value of the Y register is not altered, and the flags are not altered.