Freescale Semiconductor, Inc.
Instruction Set
Instruction Types
12.4.2 Read-Modify-Write Instructions
These instructions read a memory location or a register, modify its
contents, and write the modified value back to the memory location or to
the register.
NOTE: Do not use read-modify-write operations on write-only registers.
Table 12-2. Read-Modify-Write Instructions
Instruction
Arithmetic shift left (same as LSL)
Arithmetic shift right
Mnemonic
ASL
ASR
(1)
Bit clear
BCLR
(1)
Bit set
BSET
Clear register
CLR
COM
DEC
INC
Complement (one’s complement)
Decrement
Increment
Logical shift left (same as ASL)
Logical shift right
LSL
LSR
NEG
ROL
ROR
Negate (two’s complement)
Rotate left through carry bit
Rotate right through carry bit
Test for negative or zero
(2)
TST
1. Unlike other read-modify-write instructions, BCLR and BSET use
only direct addressing.
2. TST is an exception to the read-modify-write sequence because it
does not write a replacement value.
MC68HC705C8A — Rev. 3
MOTOROLA
Technical Data
Instruction Set
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