BSB

Purpose

transfer control to subroutine

Format

opcode displ.bx                                                branch to subroutine

opcode dst.ab                                                  jump to subroutine

Operation

-(SP) ß PC;

PC ß PC + SEXT (displ);                               branch to subroutine

PC ß dst;                                                        jump to subroutine

Condition codes

N ß N;

Z ß Z;

V ß V;

C ß C;

Exceptions

none

Opcodes

10        BSBB        Branch to Subroutine with Byte Displacement

30        BSBW       Branch to Subroutine with Word Displacement

16        JSB            Jump to Subroutine

Description

PC is pushed on the stack as a longword. For branch, the sign-extended branch displacement is added to PC and PC is replaced by the result. For jump, PC is replaced by the destination operand.

Notes

Since the operand specifier conventions cause the evaluation of the destination operand before saving PC, JSB can be used for co routine calls with the stack used for linkage. The form of such a call is JSB *(SP)+.