Intel 80286 User 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.
1-13
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Intel 80286 Specifications

General

Processor Type	Microprocessor
Clock Speed	6 MHz to 25 MHz
Transistor Count	134, 000
Addressable Memory	16 MB
Instruction Set	x86
Architecture	x86
Data Bus Width	16-bit
Address Bus Width	24-bit
Operating Modes	Real mode, Protected mode
Process Technology	1.5 µm
Voltage	5V
Introduced	1982
Package	68-pin PGA