MC68030 Datasheet, PDF (55/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Data Organization and Addressing Capabilities
2.4.13 Program Counter Indirect with Index (Base Displacement) Mode
This mode is similar to the address register indirect with index (base displacement) mode
described in 2.4.8 Address Register Indirect with Index (Base Displacement) Mode, but
the PC is used as the base register. It requires an index register indicator and an optional
16- or 32-bit sign-extended base displacement. The operand is in memory. The address of
the operand is the sum of the contents of the PC, the scaled contents of the sign-extended
index register, and the base displacement. The value of the PC is the address of the first
extension word. The reference is a program space reference and is only allowed for reads
(refer to 4.2 Address Space Types).
In this mode, the PC, the index register, and the displacement are all optional. However, the
user must supply the assembler notation "ZPC'' (zero value is taken for the PC) to indicate
that the PC is not used. This allows the user to access the program space without using the
PC in calculating the effective address. The user can access the program space with a data
register indirect access by placing ZPC in the instruction and specifying a data register (Dn)
as the index register.
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
PROGRAM COUNTER:
EA = (PC) + (Xn) + bd
(bd, PC, Xn. SIZE*SCALE)
111
011
31
0
ADDRESS OF EXTENSION WORD
31
0
BASE DISPLACEMENT:
SIGN-EXTENDED VALUE
+
31
0
INDEX REGISTER
SIGN-EXTENDED VALUE
SCALE:
7
0
SCALE VALUE
X
+
31
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
1, 2 OR 3
0
OPERAND
MOTOROLA
MC68030 USER’S MANUAL
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