Commodore Plus 4 - Page 283

The 6508 Microprocessor 271
.2008 90 01 BCC $200B If clear, skip the next instruction.
. S00A E8 INX Increment the count of bits set to 1.
. 200B 88 DEY Decrement the bit count.
. 200C 10 F9 BPL $2007 If not done, continue.
. 200E 00 BRK Stop processing.
The number of bits set to 1 is displayed in the X register when the BRK
instruction is executed.
WOP—ITo Operation
No operation is performed.
Operation: None Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Implied NOP EA 1 2
The processor performs no operation. None of the flags are affected. This
instruction is generally used as a placeholder.
Example: In this program a loop executes until a certain memory location is zero. In this
case, a zero page location (the low byte of the jiffy clock) is used. A NOP
instruction is placed just after the LD A instruction. This leaves room for testing a
location not on zero page in a subsequent execution of the program.
sooo
2002
2003
2005
A5
EA
DO
00
A5
PB
LDA
HOP
BITE
BRK
#A5
#2000
ORA—OR Memory with Accumulator
The value currently in the accumulator is logically ORed with the specified
operand, and the result is placed in the accumulator.
Operation: Av M-+ A Flags Affected: N, Z
Addressing Mode Syntax Opcode Bytes Cycles
Immediate ORA#$hh 09 2 2
Zero page ORA $hh 05 2 3
Zero page, X ORA $hh,X 15 2 4