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#### 9.22.2 Syntax

In the M68HC11 syntax, the instruction name comes first and it may be followed by one or several operands (up to three). Operands are separated by comma (‘`,`’). In the normal mode, `as` will complain if too many operands are specified for a given instruction. In the MRI mode (turned on with ‘`-M`’ option), it will treat them as comments. Example:

         inx
         lda  #23
         bset 2,x #4
         brclr *bot #8 foo

The presence of a ‘`;`’ character or a ‘`!`’ character anywhere on a line indicates the start of a comment that extends to the end of that line.

A ‘`*`’ or a ‘`#`’ character at the start of a line also introduces a line comment, but these characters do not work elsewhere on the line. If the first character of the line is a ‘`#`’ then as well as starting a comment, the line could also be logical line number directive (see Comments) or a preprocessor control command (see Preprocessing).

The M68HC11 assembler does not currently support a line separator character.

The following addressing modes are understood for 68HC11 and 68HC12:

Immediate
  ‘`#number`’
Address Register
  ‘`number,X`’, ‘`number,Y`’

  The number may be omitted in which case 0 is assumed.

Direct Addressing mode
  ‘`*symbol`’, or ‘`*digits`’
Absolute
  ‘`symbol`’, or ‘`digits`’

The M68HC12 has other more complex addressing modes. All of them are supported and they are represented below:

Constant Offset Indexed Addressing Mode
  ‘`number,reg`’

  The number may be omitted in which case 0 is assumed. The register can be either ‘`X`’, ‘`Y`’, ‘`SP`’ or ‘`PC`’. The assembler will use the smaller post-byte definition according to the constant value (5-bit constant offset, 9-bit constant offset or 16-bit constant offset). If the constant is not known by the assembler it will use the 16-bit constant offset post-byte and the value will be resolved at link time.

Offset Indexed Indirect
  ‘`[number,reg]`’

  The register can be either ‘`X`’, ‘`Y`’, ‘`SP`’ or ‘`PC`’.

Auto Pre-Increment/Pre-Decrement/Post-Increment/Post-Decrement
  ‘`number,-reg`’ ‘`number,+reg`’ ‘`number,reg-`’ ‘`number,reg+`’

  The number must be in the range ‘`-8`’..‘`+8`’ and must not be 0. The register can be either ‘`X`’, ‘`Y`’, ‘`SP`’ or ‘`PC`’.

Accumulator Offset
  ‘`acc,reg`’

  The accumulator register can be either ‘`A`’, ‘`B`’ or ‘`D`’. The register can be either ‘`X`’, ‘`Y`’, ‘`SP`’ or ‘`PC`’.

Accumulator D offset indexed-indirect
  ‘`[D,reg]`’

  The register can be either ‘`X`’, ‘`Y`’, ‘`SP`’ or ‘`PC`’.

For example:

         ldab 1024,sp
         ldd [10,x]
         orab 3,+x
         stab -2,y-
         ldx a,pc
         sty [d,sp]