GX1 datasheet(73/247 Pages) NSC

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Processor Programming (Continued)

Table 3-23. Application and System Segment Descriptors TYPE Bit Definitions

TYPE

Bits [11:8]

System Segment and Gate Types

Bit 12 = 0

Application Segment Types

Bit 12 = 1

Num

SEWA

TYPE (Data Segments)

0000

Reserved

Data

Read-Only

0001

Available 16-Bit TSS

Data

Read-Only, accessed

0010

LDT

Data

Read/Write

0011

Busy 16-Bit TSS

Data

Read/Write accessed

0100

16-Bit Call Gate

Data

Read-Only, expand down

0101

Task Gate

Data

Read-Only, expand down, accessed

0110

16-Bit Interrupt Gate

Data

Read/Write, expand down

0111

16-Bit Trap Gate

Data

Read/Write, expand down, accessed

Num

SCRA

TYPE (Code Segments)

1000

Reserved

Code

Execute-Only

1001

Available 32-Bit TSS

Code

Execute-Only, accessed

1010

Reserved

Code

Execute/Read

1011

Busy 32-Bit TSS

Code

Execute/Read, accessed

1100

32-Bit Call Gate

Code

Execute/Read, conforming

1101

Reserved

Code

Execute/Read, conforming, accessed

1110

32-Bit Interrupt Gate

Code

Execute/Read-Only, conforming

1111

32-Bit Trap Gate

Code

Execute/Read-Only, conforming accessed

SEWA/SCRA:

S = Code Segment (not Data Segment)

E = Expand Down

W = Write Enable

A = Accessed

C = Conforming Code Segment

R = Read Enable

GX1 Datasheet(PDF) 73 Page - National Semiconductor (TI)

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