HCS12 datasheet(77/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

5.20 Loop Primitive Instructions

The loop primitives can also be thought of as counter branches. The

instructions test a counter value in a register or accumulator (A, B, D, X, Y,

or SP) for zero or non-zero value as a branch condition. There are

predecrement, preincrement, and test-only versions of these instructions.

The numeric range of 9-bit offset values is $100 (–256) to $0FF (255)

from the address of the next memory location after the offset value.

Table 5-20 is a summary of loop primitive branches.

Table 5-20. Loop Primitive Instructions

Mnemonic

Function

Equation or Operation

DBEQ

Decrement counter and branch if = 0

(counter = A, B, D, X, Y, or SP)

(counter) – 1

⇒ counter

If (counter) = 0, then branch;

else continue to next instruction

DBNE

Decrement counter and branch if

≠ 0

(counter = A, B, D, X, Y, or SP)

(counter) – 1

⇒ counter

If (counter) not = 0, then branch;

else continue to next instruction

IBEQ

Increment counter and branch if = 0

(counter = A, B, D, X, Y, or SP)

(counter)

+ 1⇒ counter

If (counter) = 0, then branch;

else continue to next instruction

IBNE

Increment counter and branch if

≠ 0

(counter = A, B, D, X, Y, or SP)

(counter)

+ 1⇒ counter

If (counter) not = 0, then branch;

else continue to next instruction

TBEQ

Test counter and branch if = 0

(counter = A, B, D, X,Y, or SP)

If (counter) = 0, then branch;

else continue to next instruction

TBNE

Test counter and branch if

≠ 0

(counter = A, B, D, X,Y, or SP)

If (counter) not = 0, then branch;

else continue to next instruction

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