Motorola M68CPU32BUG, Руководство пользователя

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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.