User's Manual

OVERVIEW OF NUMERIC PROCESSING
TAG VALUES:
00 ~ VALID
01 ~ ZERO
10 ~ INVALID OR INFINITY
11 ~ EMPTY
Figure 1-6. 80287 Tag Word Format
15
CONTROL WORD
STATUS
WORD
TAG WORD
INSTRUCTION POINTER (15-0)
INSTRUCTION
;)1 'I
INSTRUCTION
POINTER
(19-16) 0
OPCODE (10-0)
DATA POINTER (15-01
DATA POINTER 1
(19-16)
0
15 1211
REAL MODE
MEMORY
OFFSET
to
+4
+6
+8·
+10
+12
15
CONTROL WORD
'.
STATUS WORD
TAG WORD
IPOFFSET
CSSELECTOR
DATA OPERAND OFFSET
DATA OPERAND SELECTOR
PROTECTED
MODE
G30108
MEMORY OFFSET
+0
+2
+4
+6
+8
+10
+12
G30108
Figure 1-7. 80287 Instruction and Data POinter Image in Memory
When stored in memory, the instruction and data pointers appear in one of two formats, depending on
the operating mode of the 80287. Figure 1-7 shows these pointers as they are stored following an
FSTENV instruction. In Real-Address mode, these values are the
20-bit physical address and ll-bit
opcode formatted like the 8087. In Protected mode, these values are the 32-bit virtual addresses used
by the program that executed the ESC instruction.
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