N386SX データシートの表示（PDF） - Intel

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N386SX

Intel387™ SX MATH COPROCESSOR

Intel 

Intel387TM SX MATH COPROCESSOR

of the static architecture It is responsible for shut-

ting down idle sections of the device to save power

Microprocessor Math CoProcessor Interface

The Intel386 CPU interprets the pattern 11011B in

most significant five bits of an instruction as an op-

code intended for a math coprocessor Instructions

thus marked are called ESCAPE or ESC instruc-

tions Upon decoding the instruction as an ESC in-

struction the Intel386 CPU transfers the opcode to

the math coprocessor through an I O write cycle at

a dedicated address (8000F8H) outside the normal

programmed I O address range The math coproc-

essor has dedicated output signals for controlling

the data transfer and notifying the CPU if the Math

CoProcessor is busy or that a floating point error has

occurred

2 3 Power Management

The Intel387 SX Math CoProcessor offers two

modes of power management dynamic and idle

2 3 1 DYNAMIC MODE

Dynamic Mode is when the device is executing an

instruction Using Intel’s CHMOS IV technology the

Intel387 SX Math CoProcessor draws considerably

less power than its predecessor The active power

supply current is reduced to approximately 100 mA

at 20 MHz and provides low case temperatures

2 3 2 IDLE MODE

When an instruction is not being executed the

Intel387 SX Math CoProcessor will automatically

change to Idle Mode Three clocks after completion

of the previous instruction the internal power man-

ager shuts down the floating point execution unit

and all non-essential circuitry Only portions of the

Bus Interface Unit remain active to monitor the CPU

bus activity and to accept the next instruction when

it is transferred When the CPU transfers the next

instruction to the Math CoProcessor the Intel387 SX

Math CoProcessor accepts the instruction and

ramps the internal core within one clock so there is

no impact to performance or throughput In idle

mode the Intel387 SX Math CoProcessor draws typ-

ically 4 mA of current and reduces case temperature

to near ambient

NOTE

In asynchronous clock mode (CKM e 0) the inter-

nal idle mode is disabled

2 4 Compatibility

The Intel387 SX Math CoProcessor is compatible

with the Intel387 SL Mobile Math CoProcessor Due

to the increased performance and internal pipelining

effects diagnostic programs should never use in-

struction execution time for test purposes

2 5 Performance

The increased performance of floating point calcula-

tions can be attributed to the 84-bit architecture and

floating point processor For the CPU to execute

floating point calculations requires very long soft-

ware emulation methods with reduced resolution

and accuracy The performance of the Intel387 SX

Math CoProcessor has been further enhanced

through improvements in the internal microcode and

through internal architectural changes These refine-

ments will increase Whetstone benchmarks by ap-

proximately 10% to 25% over the original Intel387

SX Math CoProcessor

Real performance however should be measured

with application software Depending upon software

coding system overhead and percentage of floating

point instructions performance can vary significant-

ly

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