Commodore Plus 4 - Page 256

244 Machine Language on the Commodore Plus/4
contents of $2100-$21 OB after the program executes. The values in $2108-$21 OB
will be the sum of $2100-$2103 and $2104-52107.
The carry flag is used to transmit the carry information between the bytes.
Before the first ADC, the carry is cleared, so the first result is correct. If a carry is
produced, it is automatically added into the next byte because the program does
not clear the carry before performing the next ADC.
AND—AKTD Memory with Accumulator
The value currently in the accumulator is logically ANDed to the specified
operand, and the result is placed in the accumulator.
Operation: A A M —
Addressing Mode
Immediate
Zero page
Zero page, X
Absolute
Absolute, X
Absolute, Y
(Indirect, X)
(Indirect), Y
A
Syntax
AND #$hh
AND $hh
AND $hh,X
AND Shhhh
AND $hhhh,X
AND $hhhh,Y
AND ($hh,X)
AND ($hh),Y
Flags Affected: N, Z
Opcode
29
25
35
2D
3D
39
21
31
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 both the value in the accumulator and the value in
the operand are set to 1 in the result. Bits that are cleared to 0 in either value 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 AND instruction is useful when one or more bits of a byte must be cleared to
0 while the other bits remain unchanged. This example increments the luminance
of the screen without affecting the color and times itself by looking at a single bit
in the jiffy clock timer on zero page.
. 2000 A9 00 LDA #$00 Start at zero luminance.
. 2002 85 FF STA $FP Save current luminance at $FF.
. 2004 AD 15 FP LDA $FF15 Get value of background register.
. 2007 29 OF AMD #$0F Do not change the color bits.
. 2009 05 FF 0RA IFF Put in luminance.
. 200B 8D 15 FF STA $FF15 Put value into background register.