376 datasheet(10/95 Pages) INTEL

10 / 95 page

376 EMBEDDED PROCESSOR

22 Instruction Set

The instruction set is divided into nine categories of

operations

Data Transfer

Arithmetic

ShiftRotate

String Manipulation

Bit Manipulation

Control Transfer

High Level Language Support

Operating System Support

Processor Control

These 80376 processor instructions are listed in Ta-

ble 81 80376 Instruction Set and Clock Count

Summary

All 80376 processor instructions operate on either 0

1 2 or 3 operands an operand resides in a register

in the instruction itself or in memory Most zero op-

erand instructions (eg CLI STI) take only one byte

One operand instructions generally are two bytes

long The average instruction is 32 bytes long

Since the 80376 has a 16-byte prefetch instruction

queue an average of 5 instructions can be pre-

fetched The use of two operands permits the follow-

ing types of common instructions

Memory to Register

Immediate to Register

Memory to Memory

Immediate to Memory

The operands are either 8- 16- or 32-bit long

23 Memory Organization

Memory on the 80376 is divided into 8-bit quantities

(bytes) 16-bit quantities (words) and 32-bit quanti-

ties (dwords) Words are stored in two consecutive

bytes in memory with the low-order byte at the low-

est address Dwords are stored in four consecutive

bytes in memory with the low-order byte at the low-

est address The address of a word or Dword is the

byte address of the low-order byte For maximum

performance word and dword values should be at

even physical addresses

In addition to these basic data types the 80376 proc-

essor supports segments Memory can be divided

up into one or more variable length segments which

can be shared between programs

ADDRESS SPACES

The 80376 has three types of address spaces logi-

cal linear

and physical A logical address (also

known as a virtual address) consists of a selector

and an offset A selector is the contents of a seg-

ment register An offset is formed by summing all of

the addressing components (BASE INDEX and

DISPLACEMENT) discussed in Section 24 Ad-

dressing Modes

into an effective address

Every selector has a logical base address associat-

ed with it that can be up to 32 bits in length This 32-

bit logical base address is added to either a 32-bit

offset address or a 16-bit offset address (by using

the address length prefix )to form a final 32-bit lin-

ear

address This final linear address is then trun-

cated so that only the lower 24 bits of this address

are used to address the 16 Mbytes physical memory

address space The logical base address is stored

in one of two operating system tables (ie the Local

Descriptor Table or Global Descriptor Table)

Figure 23 shows the relationship between the vari-

ous address spaces

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