MC68HC705MC4MP datasheet(152/180 Pages) FREESCALE

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Instruction Set

MC68HC705MC4 — Rev. 2.0

Instruction Set

13.4.3 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.

The BRCLR and BRSET instructions cause a branch based on the state

of any readable bit in the first 256 memory locations. These 3-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 effective branch destination by adding the third byte to the

program counter if the specified bit tests true. The bit to be tested and its

condition (set or clear) is part of the opcode. The span of branching is

from –128 to +127 from the address of the next location after the branch

instruction. The CPU also transfers the tested bit to the carry/borrow bit

of the condition code register.

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