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 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:
BASE DISPLACEMENT:
INDEX REGISTER
SCALE:
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
MOTOROLA
EA = (PC) + (Xn) + bd
(bd, PC, Xn. SIZE*SCALE)
111
011
31
SIGN-EXTENDED VALUE
31
SIGN-EXTENDED VALUE
7
1, 2 OR 3
MC68030 USER'S MANUAL
Data Organization and Addressing Capabilities
31
ADDRESS OF EXTENSION WORD
0
0
0
SCALE VALUE X
31
OPERAND
0
+
+
0
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