GX1 datasheet(82/247 Pages) NSC

82 / 247 page

www.national.com

Revision 1.0

Processor Programming (Continued)

3.6.5

Exceptions in Real Mode

Many of the exceptions described in Table 3-29 "Interrupt

Vector Assignments" on page 80 are not applicable in real

mode. Exceptions 10, 11, and 14 do not occur in real

mode. Other exceptions have slightly different meanings in

real mode as listed in Table 3-31.

3.6.6

Error Codes

When operating in protected mode, the following exceptions

generate a 16-bit error code:

• Double Fault

• Alignment Check

• Invalid TSS

• Segment Not Present

• Stack Fault

• General Protection Fault

• Page Fault

The error code format and bit definitions are shown in Table

3-32. Bits [15:3] (selector index) are not meaningful if the

error code was generated as the result of a page fault. The

error code is always zero for double faults and alignment

check exceptions.

Table 3-31. Exception Changes in Real Mode

Vector

Number

Protected Mode

Function

Real Mode

Function

Double fault.

Interrupt table limit overrun.

Invalid TSS.

Does not occur.

Segment not

present.

Does not occur.

Stack fault.

SS segment limit overrun.

General protec-

tion fault.

CS,DS, ES,FS, GS seg-

ment limit overrun. In pro-

tected mode, an error code

is pushed. In real mode, no

error code is pushed.

Page fault.

Does not occur.

Table 3-32. Error Codes

Selector Index

Table 3-33. Error Code Bit Definitions

Fault

Type

Selector Index

(Bits 15:3)

S2 (Bit 2)

S1 (Bit 1)

S0 (Bit 0)

Page

Fault

Reserved.

Fault caused by:

0 = Not present page

1 = Page-level protection

violation

Fault occurred during:

0 = Read access

1= Write access

Fault occurred during:

0 = Supervisor access

1 = User access.

IDT Fault

Index of faulty IDT

selector.

Reserved

If = 1: exception occurred while

trying to invoke exception or

hardware interrupt handler.

Segment

Fault

Index of faulty

selector.

TI bit of faulty selector

If=1:

exception occurred while trying

to invoke exception or hardware

interrupt handler.

GX1 Datasheet(PDF) 82 Page - National Semiconductor (TI)

GX1 Datasheet(HTML) 82 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL