Motorola M68CPU32BUG Manuel d'utilisateur télécharger pdf (Page 111)

ASSEMBLER/DISASSEMBLER

M68CPU32BUG/D 4-9

When specifying operands, the user may skip or omit entries with the following addressing

modes.

• Address register indirect with index, base displacement.

• Program counter indirect with index, base displacement.

For the above modes, the rules for omission/skipping are as follows:

• The user may terminate the operand by specifying ’’)’’.

EXAMPLE

CLR ( ) or

CLR (,,) is equivalent to

CLR (0.N,ZA0,ZD0.W*1)

• The user may skip a field by stepping past it with a comma.

EXAMPLE

CLR (D7) is equivalent to

CLR ($D7,ZA0,ZD0.W*1)

but

CLR (,,D7) is equivalent to

CLR (0.N,ZA0,D7.W*1)

• If the user does not specify the base register, the default is ’’ZA0’’. When Z precedes

the register number, it indicates that register is suppressed.

• If the user does not specify the index register, the default is ’’ZD0.W*1’’.

• Any unspecified displacements are defaulted to ’’0’’.

4.2.3 Define Constant Directive (DC.W)

The format for the DC.W directive is:

DC.W <operand >

This directive defines a constant in memory. The DC.W directive has only one operand (16-bit

value) which can contain the actual value (decimal, hexadecimal, or ASCII). Alternatively, the

operand can be an expression which is assigned a numeric value by the assembler. The constant

is aligned on a word boundary if word (.W) size is specified. An ASCII string is recognized when

characters are enclosed inside single quotes marks (’ . . . ’). Each character (7 bits) is assigned to a

byte of memory with the eighth bit (MSB) always equal to zero. If only one byte is entered, the

byte is right justified. A maximum of two ASCII characters may be entered for each DC.W

directive.

1 2 ... 106 107 108 109 110 111 112 113 114 115 116 ... 195 196

Pas de commentaire

Motorola M68CPU32BUG Manuel d'utilisateur Page 111