Commodore Plus 4 - Page 284

278 Machine Language on the Commodore Plus/4
Operation: Av M^ A Flags Affected: N, Z
Addressing Mode Syntax Opcode Bytes Cycles
Absolute ORAShhhh OD 3 4
Absolute, X ORA$hhhh,X ID 3 4*
Absolute, Y ORA $hhhh,Y 19 3 4*
(Indirect, X) ORA ($hh,X) 01 2 6
(Indirect), Y ORA ($hh),Y 11 2 5*
* Add 1 when a page boundary is crossed.
Those bits that are set to 1 in the value in the accumulator or set to 1 in the
operand, or both, are set to 1 in the result. Bits that are cleared to 0 in both values
are cleared to 0 in the result. If the result has the high bit set to 1, the N flag is set to
1; otherwise it is cleared to 0. If the result is zero, the Z bit is set to 1; otherwise it is
cleared to 0.
Example: The first 256 locations of color memory are set to multicolor $08. Then the OR A
instruction is used to place the graphics chip into multicolor mode. The program
waits for a key to be hit and then returns to normal mode.
2000
2002
S004
2007
2008
200A
200D
200F
2012
2015
2017
201A
201C
201P
AO
A9
99
88
DO
AD
09
8D
20
FO
AD
29
8D
00
00
08
00
FA
07
10
07
E4
FB
07
EF
07
08
FF
FF
FF
FF
FF
LDY
LDA
STA
DEY
BNE
LDA
0EA
STA
JSR
BEQ
LDA
AND
STA
BRK
##00
#$08
$0800,Y
$2004
$FF07
#$10
$FF07
$FFE4
$2012
$FF07
#$EF
$FF07
.Y indexes color memory.
.A is color to fill with.
Store color in the next color location.
Decrement the index register.
If not done, go on.
Get the current value of register 7.
Set bit 4 to 1 to turn on multicolor.
Store in register 7.
Look for a key hit.
If none, go back.
Get the current value of register 7.
Clear bit 4 to 0 to turn off multicolor.
Store in register 7.
Stop processing.
PHA—Push Accumulator onto ttie Stack
The value currently in the accumulator is pushed onto the stack.
Operation: A I . Flags Affected: None
Addressing Mode Syntax Opcode Bytes Cycles
Implied PHA 48_ 1 3