Commodore Plus 4 - Page 285

The 6502 Microprocessor
873
The value in the accumulator is stored in the location indicated by the stack
pointer, and the stack pointer is decremented.
Example: This program continuously changes the border color until a key is hit. The PH A
instruction is used to save the original color of the border on the stack for
restoration after the key hit.
2000 AD 19 FF LDA $FF19
2003 48 PHA
S004 20 OC 20 JSR $2000
2007 68 PLA
2008 8D 19 FF STA $FF19
200B 00 BRK
200C EE 19 FF INC $FF19
200F 20 E4 FF JSR $FFE4
2012 FO F8 BEQ $2000
2014 60 RTS
Get the current border color.
Save on the stack.
Execute the border color change
subroutine.
Retrieve the original border color.
Restore the original border color.
Stop processing.
Increment the border color.
Look for a key hit.
If no key, then go back.
Exit the subroutine.
PHP—Push Processor Status Register onto the Stack
The value currently in the processor status register is pushed onto the stack.
Operation: SR \
Addressing Mode Syntax
Flags Affected: None
Opcode Bytes Cycles
Implied
PHP
08
1
The value in the processor status register is stored in the location indicated by
the stack pointer, and the stack pointer is decremented.
Example: This example shows BASIC preparing to return from a SYS command. The
value of the status register returned from the user routine is saved in $07F5.
. A7CF 08
PHP
. A7D0 8D P2 07 STA $07FS
. A7D3 8E F3 07 STX $07F3
. A7D6 8C F4 07 STY $07F4
. A7D9 68 PLA
Push the returned status onto the
stack.
Save the returned .A.
Save the returned .X.
Save the returned .Y.
Pull the returned status from the
stack.