G1-233P-85-1.8
| Model | G1-233P-85-1.8 |
| Description | Processor Series Low Power Integrated x86 Solution |
| PDF file | Total 247 pages (File size: 4M) |
| Chip Manufacturer | NSC |
Geode™ GX1 Processor Series
Instruction Set
(Continued)
8.1.4.2
Table 8-9. General Registers Selected by mod r/m
Fields and w Field
16-Bit
Operation
mod
11
11
11
11
11
11
11
11
r/m
000
001
010
011
100
101
110
111
w=0
AL
CL
DL
BL
AH
CH
DH
BH
w=1
AX
CX
DX
BX
SP
BP
SI
DI
32-Bit
Operation
w=0
AL
CL
DL
BL
AH
CH
DH
BH
w=1
EAX
ECX
EDX
EBX
ESP
EBP
ESI
EDI
sreg3 Field (FS and GS Segment Register
Selection)
The sreg3 field (Table 8-12) is 3-bit field that is similar to
the sreg2 field, but allows use of the FS and GS segment
registers.
Table 8-12. sreg3 Field Encoding
sreg3 Field
000
001
010
011
100
101
110
111
Segment Register Selected
ES
CS
SS
DS
FS
GS
Undefined
Undefined
8.1.4 reg Field
The reg field (Table 8-10) determines which general regis-
ters are to be used. The selected register is dependent on
whether a 16- or 32-bit operation is current and on the
status of the w bit.
8.1.5 s-i-b Byte (Scale, Indexing, Base)
The s-i-b fields provide scale factor, indexing and a base
field for address selection. The ss, index and base fields are
described next.
8.1.5.1 ss Field (Scale Selection)
The ss field (Table 8-13) specifies the scale factor used in
the offset mechanism for address calculation. The scale
factor multiplies the index value to provide one of the com-
ponents used to calculate the offset address.
Table 8-10. General Registers Selected by reg
Field
16-Bit Operation
reg
000
001
010
011
100
101
110
111
w=0
AL
CL
DL
BL
AH
CH
DH
BH
w=1
AX
CX
DX
BX
SP
BP
SI
DI
32-Bit Operation
w=0
AL
CL
DL
BL
AH
CH
DH
BH
w=1
EAX
ECX
EDX
EBX
ESP
EBP
ESI
EDI
Table 8-13. ss Field Encoding
ss Field
00
01
01
11
Scale Factor
x1
x2
x4
x8
8.1.4.1
sreg2 Field (ES, CS, SS, DS Register
Selection)
The sreg2 field (Table 8-11) is a 2-bit field that allows one
of the four 286-type segment registers to be specified.
Table 8-11. sreg2 Field Encoding
sreg2 Field
00
01
10
11
Segment Register Selected
ES
CS
SS
DS
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