Datasheet

Central Processing Unit (CPU)
MC9S12DP256 — Revision 1.1
Central Processing Unit (CPU)
Indexed Addressing Modes
The STAR12 CPU indexed modes reduce execution time and eliminate
code size penalties for using the Y index register. STAR12 CPU indexed
addressing uses a postbyte plus zero, one, or two extension bytes after
the instruction opcode. The postbyte and extensions do the following
tasks:
• Specify which index register is used.
• Determine whether a value in an accumulator is used as an offset.
• Enable automatic pre- or post-increment or decrement
• Specify use of 5-bit, 9-bit, or 16-bit signed offsets.
Table 4 Summary of Indexed Operations
Postbyte
Code (xb)
Source Code
Syntax
Comments
rr0nnnnn
,r
n,r
–n,r
5-bit constant offset n = –16 to +15
rr can specify X, Y, SP, or PC
111rr0zs
n,r
–n,r
Constant offset (9- or 16-bit signed)
z-0 = 9-bit with sign in LSB of postbyte(s)
1 = 16-bit
if z = s = 1, 16-bit offset indexed-indirect (see below)
rr can specify X, Y, SP, or PC
111rr011 [n,r]
16-bit offset indexed-indirect
rr can specify X, Y, SP, or PC
rr1pnnnn
n,–r n,+r
n,r– n,r+
Auto pre-decrement/increment or Auto post-decrement/increment;
p = pre-(0) or post-(1), n = –8 to –1, +1 to +8
rr can specify X, Y, or SP (PC not a valid choice)
111rr1aa
A,r
B,r
D,r
Accumulator offset (unsigned 8-bit or 16-bit)
aa-00 = A
01 = B
10 = D (16-bit)
11 = see accumulator D offset indexed-indirect
rr can specify X, Y, SP, or PC
111rr111 [D,r]
Accumulator D offset indexed-indirect
rr can specify X, Y, SP, or PC
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
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