Program Counter Indirect With Index (Base Displacement) Mode - Motorola MC68030 User Manual

2.4.13 Program Counter Indirect with Index (Base Displacement) Mode
This mode is similar to the address register indirect with index (base dis-
placement) 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 prog'ram 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:
31
BASE DISPLACEMENT:
31
INDEX REGISTER:
SCALE:
EA
=
(PC) + (Xn) + bd
(bd, PC.Xn.SIZE 'SCALE)
111
011
SIGN EXTENDED VALUE
SIGN EXTENDED VALUE
31
SCALE VALUE
31
ADDRESS OF EXTENSION WORD
MEMORY ADDRESS: OPERAND
NUMBER OF EXTENSION WORDS:
1.
2. OR 3
MOTOROLA
MC68030 USER'S MANUAL
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