Freescale Semiconductor, Inc.
GENERAL RELEASE SPECIFICATION
11.2.2 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. The test for
negative or zero instruction (TST) is an exception to the read-modify-write
sequence because it does not write a replacement value. Table 11-2 lists the
read-modify-write instructions.
Table 11-2. Read-Modify-Write Instructions
Instruction
Mnemonic
ASL
Arithmetic Shift Left
Arithmetic Shift Right
Clear Bit in Memory
Set Bit in Memory
ASR
BCLR
BSET
CLR
Clear
Complement (One’s Complement)
Decrement
COM
DEC
Increment
INC
Logical Shift Left
LSL
Logical Shift Right
LSR
Negate (Two’s Complement)
Rotate Left through Carry Bit
Rotate Right through Carry Bit
Test for Negative or Zero
NEG
ROL
ROR
TST
11.2.3 Jump/Branch Instructions
Jump instructions allow the CPU to interrupt the normal sequence of the program
counter. The unconditional jump instruction (JMP) and the jump to subroutine
instruction (JSR) have no register operand. Branch instructions allow the CPU to
interrupt the normal sequence of the program counter when a test condition is
met. If the test condition is not met, the branch is not performed. All branch
instructions use relative addressing.
Bit test and branch instructions cause a branch based on the state of any
readable bit in the first 256 memory locations. These three-byte instructions use a
combination of direct addressing and relative addressing. The direct address of
the byte to be tested is in the byte following the opcode. The third byte is the
signed offset byte. The CPU finds the conditional branch destination by adding
INSTRUCTION SET
Rev. 2.0
11-5
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