376 datasheet(71/95 Pages) INTEL

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376 EMBEDDED PROCESSOR

70 DIFFERENCES BETWEEN THE

80376 AND THE 80386

The following are the major differences between the

80376 and the 80386

1 The 80376 generates byte selects on BHE and

BLE (like the 8086 and 80286 microprocessors)

to distinguish the upper and lower bytes on its

16-bit data bus The 80386 uses four-byte selects

BE0 – BE3 to distinguish between the different

bytes on its 32-bit bus

2 The 80376 has no bus sizing option The 80386

can select between either a 32-bit bus or a 16-bit

bus by use of the BS16 input The 80376 has a

16-bit bus size

3 The NA pin operation in the 80376 is identical to

that of the NA pin on the 80386 with one excep-

tion the NA pin of the 80386 cannot be activated

on 16-bit bus cycles (where BS16 is LOW in the

80386 case) whereas NA can be activated on

any 80376 bus cycle

4 The contents of all 80376 registers at reset are

identical to the contents of the 80386 registers at

reset except the DX register The DX register

contains a component-stepping identifier at reset

in 80386 after reset DH e 03H indicates 80386

DL e revision number

in 80376 after reset DH e 33H indicates 80376

DL e revision number

5 The 80386 uses A31 and MIO as a select for

numerics coprocessor The 80376 uses the

A23 and MIO to select its numerics coproces-

sor

6 The 80386 prefetch unit fetches code in four-

byte units The 80376 prefetch unit reads two

bytes as one unit (like the 80286 microproces-

sor) In BS16 mode the 80386 takes two con-

secutive bus cycles to complete a prefetch re-

quest If there is a data read or write request

after the prefetch starts the 80386 will fetch

all four bytes before addressing the new re-

quest

7 The 80376 has no paging mechanism

8 The 80376 starts executing code in what corre-

sponds to the 80386 protected mode The 80386

starts execution in real mode which is then used

to enter protected mode

9 The 80386 has a virtual-86 mode that allows the

execution of a real mode 8086 program as a task

in protected mode The 80376 has no virtual-86

mode

10 The 80386 maps a 48-bit logical address into a

32-bit physical address by segmentation and

paging The 80376 maps its 48-bit logical ad-

dress into a 24-bit physical address by segmen-

tation only

11 The 80376 uses the 80387SX numerics coproc-

essor for floating point operations while the

80386 uses the 80387 coprocessor

12 The 80386 can execute from 16-bit code seg-

ments The 80376 can only execute from 32-bit

code Segments

13 The 80376 has an input called FLT which three-

states all bidirectional and output pins including

HLDA when asserted It is used with ON Circuit

Emulation (ONCE)

80 INSTRUCTION SET

This section describes the 376 embedded processor

instruction set Table 81 lists all instructions along

with instruction encoding diagrams and clock

counts Further details of the instruction encoding

are then provided in the following sections which

completely describe the encoding structure and the

definition of all fields occurring within 80376 instruc-

tions

81 80376 Instruction Encoding and

Clock Count Summary

To calculate elapsed time for an instruction multiply

the instruction clock count as listed in Table 81 be-

low by the processor clock period (eg 50 ns for an

80376 operating at 20 MHz) The actual clock count

of an 80376 program will average 10% more

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