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XC2200 Derivatives
System Units (Vol. 1 of 2)
Central Processing Unit (CPU)
User’s Manual
4-46
V2.1, 2008-08
CPUSV2_X, V2.2
4.7.4
DSP Addressing Modes
In addition to the Standard Address Generation Unit (SAGU), the DSP Address
Generation Unit (DAGU) provides an additional set of pointer registers (IDX0, IDX1) and
offset registers (QX0, QX1). The additional set of pointer registers IDX0 and IDX1 allows
the execution of DSP specific CoXXX instructions in one CPU cycle. An independent
arithmetic unit allows the update of these dedicated pointer registers in parallel with the
GPR-pointer modification of the SAGU. The DAGU only supports indirect addressing
modes that use the special pointer registers IDX0 and IDX1.
The address pointers can be used for arithmetic operations as well as for the special
CoMOV instruction. The generation of the 24-bit memory address is different:
•
For
CoMOV
instructions, the IDX pointers are concatenated with the DPPs or the
selected page/segment address, as described for long addressing modes (see
for a summary).
•
For
arithmetic CoXXX
instructions, the IDX pointers are automatically extended to
a 24-bit memory address pointing to the internal DPRAM area, as shown in
.
Note: During the initialization of the IDX registers, instruction flow stalls are possible. For
the proper operation, refer to
IDX0
Address Pointer
SFR (FF08
H
/84
H
)
Reset Value: 0000
H
IDX1
Address Pointer
SFR (FF0A
H
/85
H
)
Reset Value: 0000
H
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
idx
0
rw
r
Field
Bits
Type
Description
idx
[15:1]
rw
Modifiable Portion of Register IDXx
Specifies the 16-bit word address pointer