IDT70T653M

High-Speed 2.5V 512K x 36 Asynchronous Dual-Port Static RAM

Industrial and Commercial Temperature Ranges

18

semaphore flags. These flags allow either processor on the left or

right side of the Dual-Port RAM to claim a privilege over the other

processorforfunctionsdefinedbythesystemdesigner’ssoftware.As

an example, the semaphore can be used by one processor to inhibit

the other from accessing a portion of the Dual-Port RAM or any other

shared resource.

TheDual-PortRAMfeaturesafastaccesstime,withbothportsbeing

completelyindependentofeachother.Thismeansthatthe activityonthe

left port in no way slows the access time of the right port. Both ports are

identicalinfunctiontostandardCMOSStaticRAMandcanbereadfrom

orwrittentoatthesametimewiththeonlypossibleconflictarisingfromthe

simultaneous writing of, or a simultaneous READ/WRITE of, a non-

semaphorelocation.Semaphoresareprotectedagainstsuchambiguous

situationsandmaybeusedbythesystemprogramtoavoidanyconflicts

inthenon-semaphoreportionoftheDual-PortRAM.Thesedeviceshave

and SEM pins control on-chip power down circuitry that permits the

respective port to go into standby mode when not selected.

Systems which can best use the IDT70T653M contain multiple

processors or controllers and are typically very high-speed systems

which are software controlled or software intensive. These ystems can

benefit from a performance increase offered by the IDT70T653Ms

hardware semaphores, which provide a lockout mechanism without

requiringcomplexprogramming.

Software handshaking between processors offers the maximum in

systemflexibilitybypermittingsharedresourcestobeallocatedinvarying

configurations. The IDT70T653M does not use its semaphore flags to

control any resources through hardware, thus allowing the system

designertotalflexibilityinsystemarchitecture.

An advantage of using semaphores rather than the more common

methods of hardware arbitration is that wait states are never incurred

in either processor. This can prove to be a major advantage in very

high-speed systems.

Functional Description

TheIDT70T653Mprovidestwoportswithseparatecontrol,address

and I/O pins that permit independent access for reads or writes to any

location in memory. The IDT70T653M has an automatic power down

downcircuitrythatpermitstherespectiveporttogointoastandbymode

when not selected (CE = HIGH). When a port is enabled, access to the

entirememoryarrayispermitted.

Interrupts

Iftheuserchoosestheinterruptfunction,amemorylocation(mail box

or message center) is assigned to each port. The left port interrupt flag

Theleftportclearstheinterruptthroughaccessofaddresslocation7FFFE

thememorylocation7FFFF.Themessage(36bits)at7FFFEor7FFFF

isuser-definedsinceitisanaddressableSRAMlocation.Iftheinterrupt

function is not used, address locations 7FFFE and 7FFFF are not used

asmailboxes,butaspartoftherandomaccessmemory.RefertoTruth

Table III for the interrupt operation.

Busy Logic

TheBUSYpinoperatesasawriteinhibitinputpin.Normaloperation

canbeprogrammedbytyingtheBUSYpinsHIGH.Ifdesired,unintended

writeoperationscanbepreventedtoaportbytyingtheBUSYpinforthat

port LOW.

Semaphores

The IDT70T653M is an extremely fast Dual-Port 512K x 36 CMOS

StaticRAMwithanadditional8addresslocationsdedicatedtobinary

NOTES:

1. This table denotes a sequence of events for only one of the eight semaphores on the IDT70T653M.

Functions

Status

No Action

1

1

Semaphore free

Left Port Writes "0" to Semaphore

0

1

Left port has semaphore token

Right Port Writes "0" to Semaphore

0

1

No change. Right side has no write access to semaphore

Left Port Writes "1" to Semaphore

1

0

Right port obtains semaphore token

Left Port Writes "0" to Semaphore

1

0

No change. Left port has no write access to semaphore

Right Port Writes "1" to Semaphore

0

1

Left port obtains semaphore token

Left Port Writes "1" to Semaphore

1

1

Semaphore free

Right Port Writes "0" to Semaphore

1

0

Right port has semaphore token

Right Port Writes "1" to Semaphore

1

1

Semaphore free

Left Port Writes "0" to Semaphore

0

1

Left port has semaphore token

Left Port Writes "1" to Semaphore

1

1

Semaphore free

5679 tbl 19