Instruction Set

Instruction Types

10.4.2 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 10-2. Read-Modify-Write Instructions

Instruction

Mnemonic

 

 

Arithmetic Shift Left (Same as LSL)

ASL

 

 

Arithmetic Shift Right

ASR

 

 

Bit Clear

BCLR(1)

Bit Set

BSET(1)

Clear Register

CLR

 

 

Complement (One’s Complement)

COM

 

 

Decrement

DEC

 

 

Increment

INC

 

 

Logical Shift Left (Same as ASL)

LSL

 

 

Logical Shift Right

LSR

 

 

Negate (Two’s Complement)

NEG

 

 

Rotate Left through Carry Bit

ROL

 

 

Rotate Right through Carry Bit

ROR

 

 

Test for Negative or Zero

TST(2)

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.

MC68HC05RC16 — Rev. 3.0

 

General Release Specification

 

 

 

MOTOROLA

Instruction Set

91