Commodore Plus 4 - Page 257

The 6508 Microprocessor 245
200E
2010
2012
2014
2016
S018
201A
201B
201D
20 IF
2021
2023
A5
29
FO
A5
29
DO
18
AS
69
85
10
00
A5
08
FA
A5
08
FA
FF
10
FF
El
LDA
AND
BEQ
LDA
AND
BNE
CLC
LDA
ADC
STA
BPL
BRK
$A5
#$08
$200E
$A5
#$08
$2014
$FF
#$10
$FF
$2004
Get low byte of jiffy clock.
Wait until bit 3 is on.
If it is still off, keep waiting.
Get low byte of jiffy clock.
Wait until bit 3 is off.
If it is still on, keep waiting.
Get ready to calculate new luminance
Get current value.
Add $10 to it to go up one luminance
level.
Save it.
If not at $80, go on.
Stop execution.
The program is executed using G 2000.
ASL-Shift Left One Bit
Each bit in the specified operand is shifted one bit to the left. The high bit is
shifted into the carry flag, and a 0 is shifted into the low bit.
Operation: C*-[7
Addressing Mode
OJ-0
Syntax
Flags Affected: N, Z, C
Opcode Bytes Cycles
Accumulator
Zero page
Zero page, X
Absolute
Absolute, X
ASL
ASL $hh
ASL $hh,X
ASL $hhhh
ASL $hhhh,X
OA
06
16
OE
IE
1
2
2
3
3
2
5
6
6
7
Bit 7 of the operand is shifted into the carry flag. Bits 6 through 0 are shifted
into bits 7 through 1, respectively. A 0 is shifted into the low bit. If the result is
negative, 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 uses the ASL instruction to move lunlinances (0 through 7) into the
high nybble of a byte so that they can be placed in the background register.
• 2000 A2 00 EDX #$00 .X will store the current luminance.
. 2002 86 FF STX $FF $FF is a temporary location for the
shifting.
. 2004 06 FF ASL $FF Shift the luminance left four times
. 2006 06 FF ASL $FF to get it into correct position