AMD Geode LX 800@0.9W - Manual (Page 625)

AMD Geode™ LX Processors Data Book 625
Instruction Set 33234H
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 components used to calculate the offset address.
8.1.5.2 Index Field (Index Selection)
The index field (Table 8-14) specifies the index register used by the offset mechanism for offset address calculation. When
no index register is used (index field = 100), the ss value must be 00 or the effective address is undefined.
Table 8-13. ss Field Encoding
ss Field Scale Factor
00 x1
01 x2
01 x4
11 x8
Table 8-14. index Field Encoding
Index Field Index Register
000 EAX
001 ECX
010 EDX
011 EBX
100 none
101 EBP
110 ESI
111 EDI