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MACRO, VAX MACRO Assembler, Operand Formats
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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Operands for instructions identify the memory locations or
the registers that are used by the machine operation. These
operands specify the addressing mode for the instruction.
The address specified is the address of the operand. The address
is stored as an absolute virtual address (compare relative mode,
where the address is stored as a displacement from the PC).
Absolute mode can be used with index mode.
@#address
address
An expression specifying an address.
The processor decrements the contents of the register by the size
of the operand data type; then the register contains the address
of the operand. The processor decrements the register by 1, 2, 4,
8, or 16 for byte, word, longword, quadword, or
octaword operands, respectively. Autodecrement mode can be used
with index mode.
-(Rn)
-(AP)
-(FP)
-(SP)
n
A number in the range of 0 through 12.
The register contains the address of the operand. After
evaluating the operand address contained in the register,
the processor increments the contents of the register by 1, 2, 4,
8, or 16 for a byte, word, longword, quadword, or
octaword respectively. Autoincrement mode can be used with index
mode.
(Rn)+
(AP)+
(FP)+
(SP)+
n
A number in the range of 0 through 12.
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4 - Autoincrement deferred
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The register contains an address that is the address of the
operand address (a pointer to the operand). After evaluating
the operand address, the processor increments the contents of the
register by 4 (the size in bytes of an address). Autoincrement
deferred mode can be used with index mode.
@(Rn)+
@(AP)+
@(FP)+
@(SP)+
n
A number in the range of 0 through 12
The address is stored as an implied displacement from the PC.
This mode can be used only in branch instructions. The
displacement for conditional branch instructions and the BRB
instruction is stored in a byte. The displacement for the BRW
instruction is stored in a word (two bytes). A byte displacement
allows a range of 127 bytes forward and 128 bytes backward. A
word displacement allows a range of 32767 bytes forward and 32768
bytes backward. The displacement is relative to the updated PC,
the byte past the byte or word where the displacement is
stored.
address
address
An expression that represents an address.
The contents of the register plus the displacement (sign-extended
to a longword) produce the address of the operand. Displacement
mode can be used with index mode.
displ(Rn)
displ(AP)
displ(FP)
displ(SP)
n
A number in the range of 0 through 12.
displ
An expression specifying a displacement; the expression can
be preceded by one of the following displacement length
specifiers, which indicate the number of bytes needed to store the
displacement.
B^ Displacement requires one byte.
W^ Displacement requires one word (two bytes).
L^ Displacement requires one longword (four bytes).
If no displacement length specifier precedes the expression, and
the value of the expression is known, the assembler chooses the
smallest number of bytes (one, two, or four) needed to store the
displacement. If no length specifier precedes the expression, and
the value of the expression is unknown, the assembler reserves one
word (two bytes) for the displacement. Note that if the
displacement is either relocatable or defined later in the source
program, the assembler considers it unknown. If the actual
displacement does not fit in the memory reserved, the Linker
displays an error message.
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7 - Displacement deferred
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The contents of the register plus the displacement (sign-extended
to a longword) produce the address of the operand address (a
pointer to the operand). Displacement deferred mode can be used
with index mode.
@displ(Rn)
@displ(AP)
@displ(FP)
@displ(SP)
n
A number in the range of 0 through 12.
displ
An expression specifying a displacement; the expression can
be preceded by one of the following displacement length
specifiers, which indicate the number of bytes needed to store the
displacement.
B^ Displacement requires one byte.
W^ Displacement requires one word (two bytes).
L^ Displacement requires one longword (four bytes).
If no displacement length specifier precedes the expression, and
the value of the expression is known, the assembler chooses the
smallest number of bytes (one, two, or four) needed to store the
displacement. If no length specifier precedes the expression, and
the value of the expression is unknown, the assembler reserves one
word (two bytes) for the displacement. Note that if the
displacement is either relocatable or defined later in the source
program, the assembler considers it unknown. If the actual
displacement does not fit in the memory reserved, the Linker
displays an error message.
The address you specify is the address of the operand. The
Linker converts the addressing mode to either relative or absolute
mode. If the address is relocatable, the Linker converts
general mode to relative mode. If the address is absolute,
the Linker converts general mode to absolute mode. You should use
general mode to write position-independent code when you do not
know whether the address is relocatable or absolute. A general
addressing mode operand requires five bytes of storage. You can
use general mode with index mode.
G^address
address
An expression specifying an address.
In both immediate and literal mode, the literal specified is
the operand. In immediate mode, the operand is stored in a byte,
word, or longword following the operand specifier. In literal
mode, the operand specifier is the operand.
#literal
The assembler selects immediate or literal mode, depending on
the value of the literal.
^I#literal
This forces immediate mode.
^S#literal
This forces literal mode. The value of the literal must be
an integer in the range 0 through 63, or one of a limited
set of floating-point numbers.
Index mode is a general register mode that can be used only
in combination with another mode (the base mode). The base mode
can be any addressing mode except register, immediate, literal,
index, or branch. The assembler first evaluates the base mode to
get the base address. To get the operand address, the assembler
multiplies the contents of the index register by the number of
bytes of the operand data type, then adds the result to the base
address.
base-mode[Rx]
base-mode[AP]
base-mode[FP]
base-mode[SP]
base-mode
Any addressing mode except register, immediate, literal, index,
or branch, specifying the base address.
x
A number in the range 0 through 12, specifying the index register.
The register contains the operand.
Rn
AP
FP
SP
n
A number in the range 0-12.
For quadword, D_floating, G_floating, or variable-bit field
operands, the operand is the contents of register n
concatenated with the contents of register n+1. For octaword and
H_floating operands, the operand is the contents of register n
concatenated with the contents of registers n+1, n+2, and n+3. In
each of these cases, the least significant bytes of the
operand are in register n and the most significant bytes are in
the highest register used.
The results of the operation are unpredictable if PC is used
in register mode or if the use of a large data type extends the
operand into the PC.
The register contains the address of the operand. Register
deferred mode can be used with index mode.
(Rn)
(AP)
(FP)
(SP)
n
A number in the range of 0 through 12.
The address specified is the address of the operand. The
assembler stores the address as a displacement from the PC.
Relative mode can be used with index mode.
address
address
An expression specifying an address; the expression can be
preceded by one of the following displacement length
specifiers, which indicate the number of bytes needed to store the
displacement.
B^ Displacement requires one byte.
W^ Displacement requires one word (two bytes).
L^ Displacement requires one longword (four bytes).
If no displacement length specifier precedes the address
expression, and the value of the expression is known, the
assembler chooses the smallest number of bytes (one, two, or four)
needed to store the displacement. If no length
specifier precedes the address expression, and the value of the
expression is unknown, the assembler uses the default
displacement length. If the address expression is either defined
later in the program or defined in another program section, the
assembler considers the value unknown.
The address specified is the address of the operand address
(a pointer to the operand). The assembler stores the address
specified as a displacement from the PC. Relative deferred mode
can be used with index mode.
@address
address
An expression specifying an address; the expression can be
preceded by one of the following displacement length
specifiers, which indicate the number of bytes needed to store the
displacement.
B^ Displacement requires one byte.
W^ Displacement requires one word (two bytes).
L^ Displacement requires one longword (four bytes).
If no displacement length specifier precedes the address
expression, and the value of the expression is known, the
assembler chooses the smallest number of bytes (one, two, or four)
needed to store the displacement. If no length
specifier precedes the address expression, and the value of the
expression is unknown, the assembler uses the default
displacement length. If the address expression is either defined
later in the program or defined in another program section, the
assembler considers the value unknown.
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