Commodore Plus 4 - Page 288

376 Machine Language on the Commodore Plus/4
. 2009 SE 00 21 ROL $2100 Rotate the next byte to the left.
. 200C 90 03 BCC $2011 If no overflow, skip the next
instruction.
. 200E EE 19 FF IWC $FF19 Increment the border color.
. 2011 00 BRK Stop processing.
Use the M (Memory) command to examine and change the values in
$2100-52103.
ROR—Rotate Right One Bit
Each bit in the specified operand is rotated one bit to the right. The low bit is
rotated into the carry flag, and the carry flag is rotated into the high bit.
Operation: p [7
Addressing Mode
Accumulator
Zero page
Zero page, X
Absolute
Absolute, X
oj-c
Syntax
ROR
ROR $hh
ROR $hh,X
ROR $hhhh
ROR $hhhh,X
Flags Affected: N, Z, C
Opcode
6 A
66
76
6E
7E
Bytes
1
2
2
3
3
Cycles
2
5
6
6
7
Bit 0 of the operand is rotated into the carry flag. Bits 7 through 1 are rotated
into bits 6 through 0, respectively. The carry flag is rotated into bit 7. If the high
bit of the result is 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 is a 4-byte shift right (division by 2). The ROR instruction is used to shift the
bits right and transmit information between bytes by means of the carry bit.
Shift the high byte to the right.
Rotate the next byte to the right.
Rotate the next byte to the right.
Rotate the next byte to the right.
Stop processing.
Use the M (Memory) command to examine and change the values in
$2100-$2103.
8000
2003
2006
2009
800C
4E
6E
6E
6E
00
00
01
02
03
21
21
21
21
LSR
ROR
ROR
ROR
BRK
$2100
$2101
$2102
$2103