Commodore Plus 4 - Page 274

Operation: A^-M -^
Addressing Mode
Immediate
Zero page
Zero page, X
Absolute
Absolute, X
Absolute, Y
(Indirect, X)
(Indirect), Y
A
Syntax
EOR #$hh
EOR $hh
EOR $hh,X
EOR Shhhh
EOR $hhhh,X
EOR $hhhh,Y
EOR ($hh,X)
EOR ($hh),Y
Flags Affected: N, Z
Opcode
49
45
55
4D
5D
59
41
51
Bytes
2
2
2
3
3
3
2
2
Cycles
2
3
4
4
4*
4*
6
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, but not both, are set to 1 in the result. Bits that are cleared to 0 in both
values or set to 1 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: This program flashes the upper left character on the screen by alternating
between the character residing there and its reverse. The EOR instruction alter
nately sets and clears the high bit to produce this result.
2000 AS 00 LDX #$00
SOOS AD 00 OC LDA $0000
S005 49 80 EOR #$80
2007 8D 00 OC STA $0000
S00A A5 A5 LDA $A5
200C 29 02
200E DO FA
2010 A5 A5
2012 29 02
2014 PO PA
2016 CA
2017 DO E9
2019 00
ATTO #$02
BETE $200A
LDA $A5
A1H) #$02
BEQ $2010
DEX
BITE $2002
BRK
.X counts 256 flashes.
Get the character in the upper left
corner.
Toggle the high bit.
Put the new character in the upper
left corner.
Now wait. Get the low byte of jiffy
clock.
Look at bit 1.
Wait until it is off.
Get the low byte of jiffy clock.
Look at bit 1.
Wait until it is on.
Decrement the flash counter.
If not done, continue.
Stop processing.