M80C286 データシートの表示（PDF） - Intel

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M80C286

HIGH PERFORMANCE CHMOS MICROPROCESSOR WITH MEMORY MANAGEMENT AND PROTECTION

Intel 

M80C286

The following comments describe possible excep-

tions side effects and allowed usage for instruc-

tions in both operating modes of the M80C286

REAL ADDRESS MODE ONLY

1 This is a protected mode instruction Attempted

execution in real address mode will result in an

undefined opcode exception (6)

2 A segment overrun exception (13) will occur if a

word operand reference at offset FFFF(H) is at-

tempted

3 This instruction may be executed in real address

mode to initialize the CPU for protected mode

4 The IOPL and NT fields will remain 0

5 Processor extension segment overrun interrupt

(9) will occur if the operand exceeds the seg-

ment limit

EITHER MODE

6 An exception may occur depending on the value

of the operand

7 LOCK is automatically asserted regardless of the

presence or absence of the LOCK instruction

prefix

8 LOCK does not remain active between all oper-

and transfers

PROTECTED VIRTUAL ADDRESS MODE ONLY

9 A general protection exception (13) will occur if

the memory operand cannot be used due to ei-

ther a segment limit or access rights violation If

a stack segment limit is violated a stack seg-

ment overrun exception (12) occurs

10 For segment load operations the CPL RPL and

DPL must agree with privilege rules to avoid an

exception The segment must be present to

avoid a not-present exception (11) If the SS reg-

ister is the destination and a segment not-pres-

ent violation occurs a stack exception (12) oc-

curs

11 All segment descriptor accesses in the GDT or

LDT made by this instruction will automatically

assert LOCK to maintain descriptor integrity in

multiprocessor systems

12 JMP CALL INT RET IRET instructions refer-

ring to another code segment will cause a gener-

al protection exception (13) if any privilege rule is

violated

13 A general protection exception (13) occurs if

CPL i 0

14 A general protection exception (13) occurs if

CPL l IOPL

15 The IF field of the flag word is not updated if CPL

l IOPL The IOPL field is updated only if

CPL e 0

16 Any violation of privilege rules as applied to the

selector operand do not cause a protection ex-

ception rather the instruction does not return a

result and the zero flag is cleared

17 If the starting address of the memory operand

violates a segment limit or an invalid access is

attempted a general protection exception (13)

will occur before the ESC instruction is execut-

ed A stack segment overrun exception (12) will

occur if the stack limit is violated by the oper-

and’s starting address If a segment limit is vio-

lated during an attempted data transfer then a

processor extension segment overrun exception

(9) occurs

18 The destination of an INT JMP CALL RET or

IRET instruction must be in the defined limit of a

code segment or a general protection exception

(13) will occur

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