US006144219A
`6,144,219
`[1] Patent Number:
`115
`United States Patent
`Palaniswami
`[45] Date of Patent:
`Nov. 7, 2000
`
`
`[54]
`
`SYSTEM AND METHOD FOR ISOLATION
`OF VARYING-POWER BACKED MEMORY
`CONTROLLER INPUTS
`
`[75]
`
`Inventor: Krishnan Palaniswami, Austin, Tex.
`
`[73] Assignee: Advanced Micro Devices, Inc.,
`Sunnyvale, Calif.
`
`[21] Appl. No.: 08/785,896
`
`[22]
`
`Filed:
`
`Jan. 21, 1997
`
`.
`Related U.S. Application Data
`
`[63] Continuation of application No. 08/548,498, Oct. 26, 1995,
`abandoned.
`
`
`
`Int. Cl.” ..
`[51]
`sees HO03K 17/16; G11C 7/00
`[52] US. Ch. voces 326/33; 365/226; 365/228;
`327/530; 327/538
`[58] Field of Search oo... 326/33, 21,9;
`327/530, 538; 365/226, 227, 228, 229
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,827,149
`5,083,293
`5,206,938
`5,226,006
`
`5/1989 Yabe oo. eeesecsscesecnseeneeees 365/229
`o..ccccccsseecsseeee 365/228
`1/1992 Gilberg et al.
`
`4/1993 Fujioka oo.
`ceseeeeee 365/228
`7/1993 Wang et al. oceans 365/228
`
`Primary Examiner—Michael Tokar
`Assistant Examiner—Anh Q. Tran
`
`[57]
`
`ABSTRACT
`
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`An isolation mechanism serves to isolate digital signal
`processor outputs from a dynamic random access memory
`controller upon the occurrence of a low power condition.
`Theisolation prevents corruption of dynamic random access
`memory due to low power. The isolation mechanism
`receives inputs of a first low power indicator and a second
`low powerindicator. The first low powerindicator pulls low
`and the second low powerindicator is forced high when a
`low power condition exists. One embodimentof the isola-
`tion mechanism includes a NANDgate connectedtoa first
`low power indicator signal and to a second low power
`indicator signal as inputs, a NOR gate connected with a
`NANDgate output as input, and a flip flop connected with
`a NOR gate output and the first low power indicator as
`inputs. The flip flop output is input to the NOR gate.
`
`4,791,614 12/1988 Arakawa oo.eecceseeseeeeneeenees 365/228
`
`13 Claims, 2 Drawing Sheets
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`v7 i4
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`POWER
`MONITOR
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`DRAM
`CONTROLLER
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`__DSPOUTPUTS |
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`DSP OUTPUTS
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`ISOLATION
`MECHANISM
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`PWDACK
`18
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`U.S. Patent
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`Nov.7, 2000
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`Sheet 1 of 2
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`6,144,219
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`U.S. Patent
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`Sheet 2 of 2
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`Nov.7, 2000
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`6,144,219
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`6,144,219
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`1
`SYSTEM AND METHOD FOR ISOLATION
`OF VARYING-POWER BACKED MEMORY
`CONTROLLER INPUTS
`
`This is a continuation, of application Ser. No. 08/548,
`498, filed Oct. 26, 1995 now abandoned.
`BACKGROUND OF THE INVENTION
`
`2
`battery power previously described. In particular, embodi-
`ments of the invention may serve to prevent corruption of
`DRAM anddata therein stored because of faulty DSP output
`signals input to a DRAM controller, attributable to lost or
`depleted battery supply. The present invention, thus, pro-
`vides significant advantages and improvementsin the art and
`technology.
`
`SUMMARYOF THE INVENTION
`
`An embodiment of the invention is an isolation mecha-
`nism. The isolation mechanism receives inputsof a first low
`powerindicator and a second low powerindicator. The first
`low powerindicator pulls low and the second low power
`indicator is forced high when powerto a device incorporat-
`ing the mechanism is low. The isolation mechanism com-
`prises a NANDgate connected, with the first low power
`indicator and the second low power indicator as inputs, a
`NORgate, connected with the NAND gate output as input,
`and a flip flop, connected with the NOR gate output and the
`first low power indicator as inputs, wherein the flip flop
`output is input to the NORgate.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a simplified, functional block illustration of a
`typical dynamic random access memory (DRAM) con-
`trolled by a battery backed DRAM controller, the controller
`receiving inputs which are outputs of a digital signal pro-
`cessor (DSP);
`FIG. 2 is a simplified, functional block illustration of a
`mechanism, according to embodiments of the present
`invention, for automatic isolation of battery backed DRAM
`controller inputs from DSP outputs, responsive to power
`shutdown, which shutdown maybetotal loss or substantial
`depletion of power; and
`FIG. 3 is a detailed schematic of the mechanism for
`
`automatic isolation shown in FIG. 2, according to embodi-
`ments of the present invention, in operation in conjunction
`with a DSP, power monitor chip, DRAM controller, and
`DRAM.
`
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
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`The present invention relates to operationsverifications in
`electronic devices powered by a varying power source and,
`more particularly,
`to a system and method of automatic
`isolation of battery backed DRAM controller inputs from
`processor outputs upon power shutdown.
`Manyelectronic devices are powered by a varying or
`fluctuating power source. A common power source for
`electronics devices is a battery. Power supplied by a battery
`varies because of depletion over timeofthe battery’s charge.
`Other power sources for electronics devices may also vary,
`either by depletion or in other manners.
`Electronics devices,
`for desired operations of those
`devices, often require power supplies that are maintained
`within certain minimum or maximum limits. This may be
`true,
`for example,
`for electronics devices incorporating
`certain processing capabilities. As power wanesor reaches
`critical limits, processor operations may vary from normal,
`expected operations. Some of the reasons for that variation
`in operations caused by power supply variations may
`include, for example, clock rate, signal timing, inappropriate
`interrupt generation, and a wide variety of others.
`Certain types of electronics devices, in particular, digital
`devices, may require or include some type of memory
`storage. There are various types of memories that are known.
`Those memories may be employed in electronics devices,
`for example, in conjunction with a processor. A particular
`type of memory, known as dynamic random access memory
`(DRAM),is a read/write type of semiconductor memorythat
`uses a capacitor as the storage cell. DRAMs must be
`repeatedly refreshed or their data will be lost. In order to
`accomplish the repeated refreshment and also to allocate
`information to DRAM storage locations, a DRAM controller
`is typically employed in conjunction with the DRAM to
`manage those functions.
`A special type of processor for electronics devices is a
`digital signal processor (DSP). DSPs may be employedin a
`Referring to FIG. 1, a typical dynamic random access
`wide variety of applications. In many of those applications,
`memory (DRAM)6 is controlled by a DRAM controller 12.
`it is desirable to use some form of memory in conjunction
`The DRAM controller 12 receives outputs 8 from a
`with the DSP, for example, for storage of DSP outputs.
`processor, such as, for example, a digital signal processor
`DRAM,for example, may serve as memory in conjunction
`(DSP) 4. The outputs 8 of the DSP 4 are inputs to the DRAM
`with DSP operations.
`50
`controller 12. The DRAM controller 12 operates to control
`DSPs,like various other processors, may perform irregu-
`the DRAM6as dictated by the DSP 4 outputs 8.
`larly when a power supply to the DSP varies. A DSP
`As may be understood,if the DSP 4, DRAM controller 12,
`powered by a battery, for example, may output floating
`and DRAM6system are powered by a varying power source
`(high-impedance) state signals when power to the DSPis
`(not shown), for example, a battery, the DSP 4, the DRAM
`lost or substantially reduced. This may occur uponatotal
`55
`controller, and the DRAM 6 maybeaffected. If the varying
`loss of poweror, as is common,whena battery power source
`powersource affects the DSP 4 operation when the power
`is depleted to a minimum,critical level of power. In that
`varies, the DSP 4 may pass undesirable outputs 8 to the
`instance of power source depletion, memory serving for
`DRAM controller 12, for example, the undesirable outputs
`DSP output storage may receive the DSPs floating state
`8 may be floating (high-impedance) state signals. Those
`output signals and, thus, the memory may contain corrupt
`outputs 8, when input to the DRAM controller 12, may
`data. This may be the case, for example, when the memory
`disturb desired operation of the DRAM controller 12.
`is DRAM. As previously mentioned, DRAM is dynamic
`memory and must be repeatedly refreshed and so is typically
`Referring now to FIG. 2, an isolation mechanism 20,
`controlled by a DRAM controller. If faulty output signals
`according to embodimentsof the present invention, is shown
`from a DSPare input to a DRAM controller, the data stored
`in use with a DSP 4 and a DRAM6controlled by a DRAM
`65
`in the DRAM controlled by the controller will be corrupted.
`controller 12. In the embodiment, the isolation mechanism
`20 is connected between the DSP 4 and the DRAM 6. In the
`The present invention overcomesthe problems associated
`with power variation, such as, for example, critically low
`
`typical configuration shown in FIG. 1, the DSP 4 outputs 8
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`connect directly to the DRAM controller 12 of the DRAM
`6. In the embodiment of the present invention, in FIG. 2,
`however,
`the DSP outputs 8 connect with the isolation
`mechanism 20 and the isolation mechanism 20 outputs 8
`connect connects with the DRAM controller 12. As in the
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`4
`inverter 21 is an input to an AND gate 22. The PWDACK
`signal 18 is the other input to the AND gate 22. The output
`of the AND gate 22 is an input to a NOR gate 24. The other
`input to the NOR gate 24 is the output of the SR latch 28,
`as hereinafter described.
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`The output of the NOR gate 24 passes to a second inverter
`26. The output of the second inverter 26 is another input to
`the SR latch 28. The output of the SR latch 28 is branched.
`One branch connects the second input to the NORgate 24.
`The branchis also an output 32 of the isolation mechanism
`20. The other branch of the SR latch 28 is input to a third
`inverter 30. The output 34 of the third inverter 30 is another
`output of the isolation mechanism 20.
`In operation of the isolation mechanism 20, according to
`the embodiment, when the PWDNsignal 16 from the power
`monitor chip 14 (shown in FIG. 2) goes active low and the
`PWDACKsignal 18 from the DSP 4 (shownin FIG. 2) goes
`high because of a low powercondition, the two signals after
`being ANDed,form a signal used to set the SR latch 28. The
`output of the SR latch 28 then pulls the Set input of the SR
`latch 28 to logic high and isolates the output from the
`PWDACKsignal 18 using the AND 22 gate and NOR 24
`gate complex gate. When the V... drops to zero, therefore,
`the floating state of the PWDACKoutputandall of the other
`outputs 8 from the DSP4 are isolated from and can notaffect
`the operation of the DRAM controller 12 (shown in FIG. 2).
`When sufficient power is resumed, the PWDNsignal 16
`is forced logic high by the power monitor chip 14 (shown in
`FIG. 2) and the SRlatch 28 is reset. The inputs to the DRAM
`controller 12 are then openedto accept the DSP 4 outputs 8.
`It is to be understood that multiple variations, changes and
`modifications are possible in the aforementioned embodi-
`ment of the invention described herein. Although certain
`illustrative embodiments of the invention have been shown
`
`typical configuration, the DRAM controller 12 controls the
`memory storage functions of the DRAM 6.
`The isolation mechanism 20 is particularly configured
`with the DSP 4 and the DRAM controller 12 in order to
`receive the DSP 4 outputs 8 before those outputs 8 pass to
`the DRAM controller 12. Because of this configured loca-
`tion of the isolation mechanism 20, the outputs 8 of the DSP
`4 may beselectively isolated by the isolation mechanism 20
`from passage to the DRAM controller 12.
`Although a wide variety of processors could be isolated in
`similar manners from various types of memory, a particu-
`larly useful application of the isolation mechanism 20 is in
`connection with the DSP 4, the DRAM controller 12, and the
`DRAM 6. Oneparticular embodiment employsthe isolation
`mechanism 20 with an ADSP 2171 digital signal processor
`obtainable from Advanced Micro Devices, Inc. That par-
`ticular processor emits a power down acknowledged
`(PWDACK)signal 18 indicative of a low power condition.
`In addition to the PWDACKsignal 18 as an indicator of the
`low powercondition, the DSP 4 may be connected to and
`monitored by a power monitor chip 14, as those skilled in the
`art will know and appreciate. The power monitor chip 14
`may output a power down (PWDN)signal 16 when low
`poweris indicated. When those signals 16, 18 are active, a
`low powercondition exists, and the isolation mechanism 20
`isolates the DRAM controller 12 so that it does not receive
`outputs 8 from the DSP 4.
`As has been stated, the DRAM controller 12 serves to
`and described here, a wide range of modification, change,
`direct signals for DRAM 6 storage into appropriate memory
`and substitution is contemplated in the foregoing disclosure
`elements 15 of the DRAM 6. Byisolating the DSP 4 outputs
`8, in the aforedescribed manner, from the DRAM controller
`and, in some instances, some features of the present inven-
`12 at the isolation mechanism 20, the DRAM controller 12
`tion may be employed without a corresponding use of the
`does not receive as inputs to it any of the outputs 8 of the
`other features. Accordingly, it is appropriate that the fore-
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`DSP 4. Because the outputs 8 of the DSP4are isolatedat the going description be construed broadly and understood as
`isolation mechanism 20, the outputs 8 do not pass to the data
`being given by way of illustration and example only, the
`of DRAM controller 12 and so do not corrupt the DRAM 6.
`spirit and scope of the invention being limited only by the
`appended claims.
`Now referring to FIG. 3, a schematic diagram of the
`Whatis claimedis:
`isolation mechanism 20 is shown in detail. The isolation
`1. An isolation circuit for isolating data input to a memory
`mechanism 20, according to certain embodiments, is a logic
`controller device during low power conditions, comprising:
`circuit which receives the PWDNsignal 16 from the power
`a first low powerindicator input signal having an active
`monitor chip 14 (shown in FIG. 2) upon a low power
`state;
`condition. In the embodiment, upon sensing the low power
`a second low power indicator input signal having an
`condition, the power monitor chip 14 sends an active low
`active state;
`signal as the PWDNsignal 16. Also upon the low power
`condition, the DSP 4 (shown in FIG. 2) operationis inter-
`a digital logic blcok having an output and havingafirst
`rupted from its normal operation through a non-maskable
`input connected to said first low powerindicator signal
`low power (PWD) hardwareinterrupt (not shownin detail).
`and a second inut connected to said second low power
`After receiving the interrupt, the DSP 4 performs certain
`indicator signal, and having a NAND gate an input
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`necessary operations in the interrupt routine to save relevant
`connectedto said first low powerindicator input signal,
`data into DRAM6andthen goes into a power downstate.
`a NORgate with an input connected to an output of said
`At that point, the power down state of the DSP 4 is then
`NANDgate, and a Flip-Flop with one input connected
`indicated by raising the PWDACKsignal 18 to an active
`to an output of said NOR gate and another input
`high signal. In any instance of full power loss, the DSP 4
`connected to said first low powerindicator input signal;
`output pin that delivers the PWDACKsignal 18 then floats
`wherein in response to said first and said second low
`in a tri-state condition.
`power indicator input signals entering its respective
`active state, said output of said digital
`logic block
`enters a logic state to signify a lower power condition
`has occurred.
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`The isolation mechanism 20 takes as inputs the PWDN
`signal 16 from the power monitor chip 14 (shownin FIG. 2)
`and the PWDACKsignal 18 from the DSP 4. The PWDN
`signal 16 is split into two branches. One branch connects to
`a first inverter 21 and the other branch connects to a flip flop,
`for example, an SR latch 28. The output from the first
`
`2. The isolation circuit of claim 1, wherein an output of
`said Flip-Flop is connected to another input of said NOR
`gate.
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`3. A low power memoryfresh isolation system, compris-
`ing:
`a) a first low powerindicator input signal having an active
`state;
`b) a second low powerindicator input signal having an
`active state;
`c) a digital logic block having an output and havinga first
`input connected to said first low powerindicator signal
`and a second input connected to said second low power
`indicator signal;
`d) a DSP circuit having data output signals and a first low
`powerindicator signal output;
`e) a power monitor circuit having a second low power
`indicator signal output;
`f) a memory data refresh controller circuit having data
`inputs connected to said DSP data outputs, having an
`input connected to said second low power indicator
`signal output, and having data outputs;
`wherein in response to the event when said first and
`second low power indicator input signals each enter
`their respective active state, said memory data refresh
`controller circuit data ouputs become disabled.
`4. The low power memoryrefresh isolation system of
`claim 3, further comprising a memory circuit having data
`inputs connected to said memory data refresh controller
`circuit data outputs.
`5. The low power memoryrefresh isolation system of
`claim 3, wherein said memory data refresh controller circuit
`comprises a DRAM controller circuit.
`6. The low power memoryfresh isolation system of claim
`4, wherein said memorycircuit comprises a DRAM.
`7. The low power memoryrefresh isolation system of
`claim 3, wherein saidfirst low powerindicating input signal
`has a first active state and said second low powerindicator
`input signal has a secondactivestate.
`8. The low power memoryrefresh isolation system of
`claim 7, wherein said first active state has a logical value
`opposite that of said second active state.
`9. A method of isolating data output from a memory
`refresh device from a memorycircuit input during periods of
`low power, comprising the steps of:
`
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`a) providing a data refresh isolation circuit;
`b) providing a memory data refresh circuit;
`c) providing a DSPcircuit;
`d) inputting DSP data from said DSP circuit to said data
`refresh isolation circuit;
`e) providing a plurality of low power indicator signals,
`each having a respective active state,
`to said data
`refresh isolation circuit;
`from said data refresh
`f) disabling DSP data output
`isolation circuit in response to the event when said
`plurality of low popwerindicator signals all enter their
`respective active state, indicating a low power condi-
`tion has occurred.
`
`10. The method of claim 9, further comprising the step of
`providing a memorycircuit having data inputs connected to
`said DSP data output from said data refresh isolation circuit.
`11. The method of claim 9, wherein at least one of said
`plurality of low powerindicator signals is output from a
`power monitor circuit.
`12. The method of claim 9, wherein at least one of said
`plurality of low powerindicator signals is output from said
`DSPcircuit.
`
`from a
`13. An arrangement of isolating data output
`memory refresh device from a memory circuit input during
`periods of low power, comprising:
`meansfor isolating a data fresh;
`refresh meansfor refreshing memory data;
`DSP meansfor processing digital signals;
`meansfor passing data from the DSP meansto the refresh
`means;
`
`signaling means for outputting a plurality of lower power
`indicator signals, each having a respective active state,
`to the refresh means;
`means, responsiveto each of the plurality of lower power
`indicator signals entering its active state, for disabling
`data from passing from the DSP meansto the refresh
`means.
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