M68HC11-Branch - Using as
Description: Using as

Up: M68HC11-opcodes

##### 9.24.6.1 Branch Improvement

Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that reach the target. Generally these mnemonics are made by prepending ‘`j`’ to the start of Motorola mnemonic. These pseudo opcodes are not affected by the ‘`--short-branches`’ or ‘`--force-long-branches`’ options.

The following table summarizes the pseudo-operations.

                                 Displacement Width
              +-------------------------------------------------------------+
              |                     Options                                 |
              |    --short-branches           --force-long-branches         |
              +--------------------------+----------------------------------+
           Op |BYTE             WORD     | BYTE          WORD               |
              +--------------------------+----------------------------------+
          bsr | bsr <pc-rel>    <error>  |               jsr <abs>          |
          bra | bra <pc-rel>    <error>  |               jmp <abs>          |
         jbsr | bsr <pc-rel>   jsr <abs> | bsr <pc-rel>  jsr <abs>          |
         jbra | bra <pc-rel>   jmp <abs> | bra <pc-rel>  jmp <abs>          |
          bXX | bXX <pc-rel>    <error>  |               bNX +3; jmp <abs>  |
         jbXX | bXX <pc-rel>   bNX +3;   | bXX <pc-rel>  bNX +3; jmp <abs>  |
              |                jmp <abs> |                                  |
              +--------------------------+----------------------------------+
         XX: condition
         NX: negative of condition XX

`jbsr`
`jbra`
  These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target.
`jb`XX
  Here, ‘`jbXX`’ stands for an entire family of pseudo-operations, where XX is a conditional branch or condition-code test. The full list of pseudo-ops in this family is:

                 jbcc   jbeq   jbge   jbgt   jbhi   jbvs   jbpl  jblo
                 jbcs   jbne   jblt   jble   jbls   jbvc   jbmi

  For the cases of non-PC relative displacements and long displacements, `as` issues a longer code fragment in terms of NX, the opposite condition to XX. For example, for the non-PC relative case:

                    jbXX foo

  gives

                     bNXs oof
                     jmp foo
                 oof: