9.24.2 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]