WO2004070786A2 - Detection circuit for mixed asynchronous and synchronous memory operation - Google Patents
Detection circuit for mixed asynchronous and synchronous memory operation Download PDFInfo
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- WO2004070786A2 WO2004070786A2 PCT/US2004/002612 US2004002612W WO2004070786A2 WO 2004070786 A2 WO2004070786 A2 WO 2004070786A2 US 2004002612 W US2004002612 W US 2004002612W WO 2004070786 A2 WO2004070786 A2 WO 2004070786A2
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/38—Information transfer, e.g. on bus
- G06F13/42—Bus transfer protocol, e.g. handshake; Synchronisation
- G06F13/4204—Bus transfer protocol, e.g. handshake; Synchronisation on a parallel bus
- G06F13/4234—Bus transfer protocol, e.g. handshake; Synchronisation on a parallel bus being a memory bus
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/14—Handling requests for interconnection or transfer
- G06F13/16—Handling requests for interconnection or transfer for access to memory bus
- G06F13/1668—Details of memory controller
- G06F13/1689—Synchronisation and timing concerns
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/14—Handling requests for interconnection or transfer
- G06F13/16—Handling requests for interconnection or transfer for access to memory bus
- G06F13/1668—Details of memory controller
- G06F13/1694—Configuration of memory controller to different memory types
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/38—Information transfer, e.g. on bus
- G06F13/42—Bus transfer protocol, e.g. handshake; Synchronisation
- G06F13/4204—Bus transfer protocol, e.g. handshake; Synchronisation on a parallel bus
- G06F13/4234—Bus transfer protocol, e.g. handshake; Synchronisation on a parallel bus being a memory bus
- G06F13/4243—Bus transfer protocol, e.g. handshake; Synchronisation on a parallel bus being a memory bus with synchronous protocol
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
- G11C11/40615—Internal triggering or timing of refresh, e.g. hidden refresh, self refresh, pseudo-SRAMs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/4063—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing or timing
- G11C11/407—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing or timing for memory cells of the field-effect type
- G11C11/4076—Timing circuits
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/41—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming static cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger
- G11C11/413—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing, timing or power reduction
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
- G11C7/10—Input/output [I/O] data interface arrangements, e.g. I/O data control circuits, I/O data buffers
- G11C7/1015—Read-write modes for single port memories, i.e. having either a random port or a serial port
- G11C7/1045—Read-write mode select circuits
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
- G11C7/10—Input/output [I/O] data interface arrangements, e.g. I/O data control circuits, I/O data buffers
- G11C7/1072—Input/output [I/O] data interface arrangements, e.g. I/O data control circuits, I/O data buffers for memories with random access ports synchronised on clock signal pulse trains, e.g. synchronous memories, self timed memories
Definitions
- the present invention is related generally to the field of integrated circuits, and more particularly, to circuitry for detecting asynchronous and synchronous memory operations in a memory device.
- pseudo-static memory are typically memory devices that are functionally equivalent to static random access memory (SRAM) devices, but have a memory core based on conventional dynamic random access memory (DRAM) cells. In general, these memory devices can be operated in the same manner one would operate a conventional SRAM. As is well known in the art, a major distinction between the two types of memory cells is that DRAM memory cells need to be periodically refreshed to maintain the stored data, whereas SRAM memory cells do not. Consequently, pseudo-static memory devices include internal refresh circuitry to perform the necessary refresh operations of the DRAM memory core. However, refresh operations are transparent to the user, so that the devices appear as not needing refresh operations.
- DRAM memory core over an SRAM memory core because of the need for periodic refresh operations to be performed, there are, however, significant advantages in other respects.
- memory density for a DRAM memory array can be much greater than that for a SRAM memory array.
- a DRAM memory cell only one transfer gate and a storage device, typically a capacitor, is necessary to store one bit of data.
- conventional SRAM memory cells can have as many as six transistors per memory cell.
- the simple structure and smaller size of DRAM memory cells translate into less complicated manufacturing processes, and consequently, lower fabrication costs when compared to the SRAM memory cell.
- memory devices employing DRAM memory cores are considerably cheaper than SRAM memory devices having equivalent memory capacities.
- a DRAM access cycle begins with a row of memory cells in the array being activated, and the respective charge state of the memory cells for the activated row are sensed and amplified.
- a particular memory cell is selected by coupling a column to an input/output line. Consequently, the memory cell at the intersection of the activated row and the selected column is accessed. At this time, data can be read from or written to the particular memory cell.
- the row of memory cells is deactivated, thus, the charge states that were initially sensed and amplified are stored by the respective capacitors of the memory cells.
- the process of sensing the charge state of the memory cells is destructive. Unless the DRAM access cycle is completed by amplifying the charge state and properly deactivating the row, the data stored by the memory cells of the activated row will be lost.
- the DRAM access cycle is completed by amplifying the charge state and properly deactivating the row, the data stored by the memory cells of the activated row will be lost.
- the DRAM access cycle is completed by amplifying the charge
- SRAM sense operation is non-destructive and does not have the same type of access cycle as a conventional DRAM memory device. Consequently, random memory addresses may be asserted to the SRAM memory device without timing restriction, and data is always expected to be returned in a certain time thereafter. This time is typically referred to as the address access time .
- a A- Yet another difference between memory devices having an SRAM memory core and those having a DRAM memory is that access times for DRAM memory cores are generally longer than the access times for SRAM memory cores.
- Asynchronous access of a DRAM memory core requires more time to provide valid data because of the time required to complete the access cycle.
- conventional DRAM devices often provide advanced access modes to decrease average access times, such as page mode access, valid memory addresses must nevertheless be provided for each data access. As a result, the minimum access time of a memory device will be limited by the setup time for providing valid and stable memory addresses, which in some cases, can take a relatively long time.
- Synchronous DRAM (SDRAM) devices which operate according to a periodic clock signal and have pipelined architectures to provide shorter average access times than asynchronous DRAM devices.
- Memory access times for SDRAM devices are generally lower because the pipelining of internal memory operations allow for different stages of a DRAM memory access operation to be executed in parallel, as well known in the art. This allows for new memory commands to be initiated prior to the completion of previous memory commands.
- conventional SDRAM devices can provide modes of operation that cannot be replicated by their asynchronous DRAM counterparts. For example, SDRAM devices have a data burst mode where new data can be output each period of a clock signal after an initial memory access without the need to provide any memory addresses other than for the first memory location.
- circuitry it is desirable for the circuitry to automatically detect whether an asynchronous or synchronous memory access operation is requested without the use of a flag or dedicated control signal that instructs the memory device to expect an asynchronous or synchronous memory access operation, hi this manner, a memory device having such circuitry can be used as a companion device with existing types of conventional memory devices.
- the present invention is directed to a memory access mode detection circuit that detects and initiates memory access modes for a memory device receiving memory address signals, control signals and a clock signal.
- the memory access mode detection circuit includes a mode detection circuit that receives the memory address signals, the control signals, and the clock signal.
- the mode detection circuit generates a first mode detection signal in response to receipt of the memory address signals or a first combination of control signals, which can indicate an asynchronous access request.
- a delay circuit further included in the memory access mode detection circuit is coupled to the mode detection circuit and generates a delayed first mode detection signal a time delay after receipt of the first mode detection signal to initiate a first mode access operation.
- the mode detection circuit further generates a second mode detection signal to initiate a second mode memory access operation in response to receipt to a second combination of control signals and an active clock signal, which can indicate a synchronous access request.
- the delay circuit In response to receiving the second mode detection signal, the delay circuit resets the time delay and does not generate the delayed first mode detection signal, in effect canceling the asynchronous access and starting a synchronous access instead.
- a method for initiating a memory access operation in a memory device receiving memory address signals, control signals and a clock signal is provided.
- a first mode detection pulse is generated in response to receiving memory address signals or a combination of control signals indicative of a first mode memory access operation, which can represent an asynchronous access.
- a first mode activation pulse to initiate the first mode memory access operation is generated a time delay following the first mode detection pulse.
- a second mode detection pulse is generated in response to receiving a clock signal and a second combination of the control signals indicative of a second mode memory access operation, which can represent a synchronous transaction. The second mode detection pulse is then used to suppress the generation of the delayed first mode detection pulse, and initiate the second mode memory access operation.
- Figure 1 is a functional block diagram of an asynchronous/synchronous detection circuit according to an embodiment of the present invention.
- Figure 2 is a functional block diagram of an embodiment of a delay circuit that can be used in the detection circuit of Figure 1.
- Figure 3 is a signal timing diagram illustrating various signals applied to the detection circuit of Figure 1.
- Figure 4 is a functional block diagram of a portion of a memory device including an asynchronous/synchronous detection circuit according to an embodiment of the present invention.
- Figure 5 is a functional block diagram of a computer system including memory devices of Figure 4.
- FIG. 1 illustrates an asynchronous/synchronous mode detection circuit 100 according to an embodiment of the present invention.
- the detection circuit 100 can be employed in a memory device that is functionally equivalent to an SRAM device, but uses a DRAM memory core.
- a significant benefit provided by embodiments of the present invention is the automatic detection of synchronous/asynchronous operation.
- the detection circuit 100 also allows for the memory device to be operated synchronously as well.
- asynchronous mode detection circuitry 110 to which address signals ADDR ⁇ 0:n> and control signals are provided.
- control signals provided to the asynchronous mode detection circuitry 110 include conventional control signals, such as a chip enable signal CE*, an address valid signal ADV*, an output enable signal OE*, and a write enable signal WE*.
- the asterisk "*" indicates that the respective control signal is an active low signal, that is, the signal is considered active when at a LOW logic level.
- the ADDR ⁇ 0:n> signals and the CE*, ADV*, OE*, and WE* signals are conventional, and are known by those of ordinary skill in the art.
- synchronous mode detection circuitry 120 receives the CE*, ADV*, OE*, and WE* signals.
- the synchronous mode detection circuitry 120 also receives a periodic clock signal CLK that is used by the synchronous mode detection circuitry 120 to synchronize operation of the memory device.
- the synchronous mode detection circuitry 120 includes control signal latches (not shown) that latch the logic state of the CE*, ADV*, OE*, and WE* signals in response to transitions of the CLK signal, such as the rising edge of the CLK signal, the falling edge of the CLK signal, or in some embodiments, on both the rising and falling edges of the CLK signal.
- the asynchronous mode detection circuitry 110 and the synchronous mode detection circuitry 120 are of conventional design known by those of ordinary skill in the art.
- control signals have been provided by way of example, and that alternative control signals may be provided to the asynchronous mode detection circuitry 110 and the synchronous mode detection circuitry 120 without departing from the scope of the present invention.
- a refresh timer 130 is also included in the detection circuit 100.
- the refresh circuit 130 is coupled to receive a pulse PULSE_ASYNC from the asynchronous mode detection circuitry 110 and a pulse PULSE_SYNC from the synchronous control circuitry 110.
- the refresh timer 130 generates an output pulse PULSE_OUT a time delay t d after the falling edge of the last (i.e., most recent) PULSE_ASYNC pulse from the asynchronous mode detection circuitry 110.
- a two-input Boolean logic OR gate 140 is coupled to receive the PULSE_OUT and PULSE_SYNC pulses from the refresh timer 130 and the synchronous mode detection circuitry 120, respectively.
- An output of the OR gate 140 is coupled to provide an activation pulse ACTJPULSE to conventional DRAM activation circuitry 150 in order to initiate an access operation in the DRAM memory core (not shown).
- a memory access operation is initiated in a conventional SRAM device by enabling the SRAM device with an active (LOW logic level) CE* signal, and asserting a memory address.
- an ADV* signal is used to indicate to the SRAM that the memory address is valid, and can be latched to initiate the memory operation.
- the type of access that is, whether a read operation or a write operation is executed, is controlled by the logic levels of the other control signals. For example, a read operation is typically executed in response to the WE* signal having a HIGH logic state at the time the memory address is asserted. In contrast, a write operation is executed in response to the WE* signal having a LOW logic state at the time the address is asserted.
- read data is expected to be returned from the memory device a certain time after the asserted memory address has been held valid for the minimum time.
- the maximum time required for the read data to be returned is typically referred to as the address access time .AA- m the event a new address is asserted before the access operation is complete, the previous access operation is aborted, and a new access operation is initiated for the memory location of the newly asserted address.
- the detection circuit 100 can be employed to accommodate the use of a DRAM memory core with a conventional SRAM memory interface.
- the detection circuit 100 can be used in a memory device having a conventional DRAM memory core to convert randomly scheduled address transitions, which conventionally used to initiate SRAM access operations, into scheduled events that are suitable for conventional DRAM memory cores.
- the detection circuit 100 further provides a mechanism for memory devices having conventional DRAM memory cores to be accessed both asynchronously in the manner of an SRAM address interface as well as synchronously to provide the benefits of conventional synchronous DRAM devices.
- the operation of the detection circuit 100 will be discussed with respect to an asynchronous access operation of a conventional SRAM address interface, followed by a synchronous memory access operation, and then a memory access operation where an asynchronous access operation is immediately followed by a synchronous access operation.
- a memory access operation that includes transitioning from an asynchronous to a synchronous memory access operation can be referred to as a mixed mode operation.
- Embodiments of the present invention automatically detect transitions in mixed mode operations. That is, detection of asynchronous and synchronous memory access operations can be made without any externally supplied flags that instruct a memory device to expect either an asynchronous or synchronous memory access operation.
- a memory access to an SRAM device is initiated upon activating the memory device by a LOW CE* signal and asserting a memory address.
- the asynchronous mode detection circuitry 110 upon receiving a newly asserted memory address and a LOW CE* signal, the asynchronous mode detection circuitry 110 generates a PULSE-SYNC pulse that is provided to the refresh timer 130 to initiate the time delay t .
- the refresh timer 130 After the time t d has elapsed, the refresh timer 130 generates a PULSE_OUT pulse that is provided through the OR gate 140 as the ACT_PULSE pulse to the DRAM activation circuits 150.
- the DRAM activation circuits 150 initiate an access operation to the memory location in the DRAM memory core corresponding to the memory address asserted to the asynchronous mode detection circuitry 110.
- the asynchronous mode detection circuitry 110 generates a PULSE_ASYNC pulse in response to receiving a new memory address, regardless of whether the new memory address is being asserted prior to the completion of a memory access cycle.
- the refresh timer 130 inserts a time delay t d of suitable length to ensure that any previously initiated memory access operation will have sufficient time to complete.
- the time delay t d is reset so that the delay is measured from receipt of the most recent PULSE_ASYNC pulse.
- the refresh timer 130 ensures that a memory access operation will not be interrupted prior to its completion. That is, since the time t d is always reset upon the receipt of a PULSE_ASYNC pulse, the refresh timer 130 ensures that an ACT_PULSE (i.e., a PULSE__OUT pulse) will not be provided to the DRAM activation circuits 150 in response to the assertion of a memory address any sooner than the time t has elapsed, which, as previously discussed, is selected to allow a memory access operation to complete.
- the delay td is approximately 25 ns, which still allows for a memory device employing a DRAM memory core to have an access time t AA of 60 ns.
- FIG. 2 illustrates a delay circuit timer 220 that can be included in the refresh timer 130 ( Figure 1).
- the delay circuit 220 includes a plurality of delay stages 240. Each delay stage 240 has a delay input and a reset input, and further has a delay output.
- a reset circuit (not shown) also included in the refresh timer will be used to reset the delay circuit timer 220 in response to receiving a PULSE_SYNC pulse from the synchronous mode detection circuit 120.
- the reset circuit which can be designed by those ordinarily skilled in the art, will not be discussed with respect to the delay circuit timer 220 in order to avoid unnecessarily complicating the description of the delay circuit timer 220.
- a delay stage 240 provides an output signal that is similar to the signal applied to the delay input except that it is delayed by a time - dd .
- a first delay stage 240 receives the PULSE_ASYNC signal at both its delay input and reset input. Subsequent delay stages 240 are coupled such that the delay input is coupled to the delay output of the previous delay stage 240.
- the reset input of each of the delay stages 240 is coupled to receive the PULSE_ASYNC signal, and the delay output of the last delay stage 240 is coupled to a first input of a two-input NOR gate 250.
- a second input of the NOR gate 250 is coupled to receive the PULSE_ASYNC signal.
- An output of the NOR gate 250 is coupled to a conventional pulse generator 254 through an inverter 252.
- the pulse generator 254 generates the pulse PULSE_OUT in response to the falling edge of the signal output by the inverter 252.
- the PULSE_OUT signal is provided to the DRAM activation circuits 150 through the OR gate 140 to start an access operation to a conventional DRAM memory core.
- the delay circuit 220 generates a PULSE_OUT pulse a time delay t d after the falling edge of the most recent PULSE_ASYNC pulse.
- the time delay t d is approximately the sum of the delay tdd of each delay stage 240. hi an effort to simplify explanation of the delay circuit 220, any gate delays have been ignored.
- the delay circuit 220 receives an PULSE_ASYNC pulse, on the falling edge of the PULSE_ASYNC pulse, the delay circuit begins counting the time delay t d . That is, for the first delay stage 240 in the chain, its delay output will go LOW t d after the falling edge of the PULSE_ASYNC pulse. The delay output of the second delay stage 240 will go LOW t dd after the falling edge of the delay output of the first delay stage 240. Thus, the falling edge of the PULSE_ASYNC pulse will trickle through the chain of delay stages 240 until being applied to the input of the NOR gate 250.
- the pulse generator 254 then generates a PULSE_OUT pulse.
- the delay stages 240 of the timing chain are reset by causing the delay output of each of the delay stages 240 to go HIGH again in response to the new PULSE_AS YNC pulse.
- the t countdown will begin again in response to the falling edge of the new PULSE_ASYNC pulse, as previously described.
- the pulse generator 254 will not generate a PULSE_OUT pulse until t d after the falling edge of the last PULSE_ASYNC pulse provided to the delay circuit 220.
- the delay circuit 220 is provided in commonly assigned, co-pending U.S. Patent Application No. 10/102,221, entitled ASYNCHRONOUS INTERFACE CIRCUIT AND METHOD FOR A PSEUDO- STATIC MEMORY DEVICE to Lovett et al, filed March 19, 2002. It will be appreciated, however, that the refresh timer 130 can include delay circuitry other than that shown in Figure 2, that is well known by those of ordinary skill in the art.
- the detection circuit 100 includes synchronous mode detection circuitry 120 that can be used to initiate synchronous memory access operations of a conventional DRAM memory core.
- synchronous mode detection circuitry 120 that can be used to initiate synchronous memory access operations of a conventional DRAM memory core.
- CLK periodic clock signal
- the synchronous mode detection circuitry 120 is conventional in design, and the design of suitable synchronous mode detection circuitry 120 is known by those of ordinary skill in the art.
- the synchronous control circuitry Upon receiving the correct combination of logic signals of the control signals, and provision of a CLK signal, the synchronous control circuitry generates a PULSE_SYNC pulse that is provided to the refresh timer 130 and the OR gate 140.
- the resulting PULSE_SYNC pulse is provided to the DRAM activation circuits 150 through the OR gate 140 as the ACTJPULSE, which initiates memory access to the DRAM memory core.
- the synchronous mode detection circuitry 120 provides internal control signals (not shown) in addition to the PULSE_SYNC pulse shown in Figure 1 in order to execute a synchronous memory access operation.
- the internal control signals are conventional in nature, and have not been shown in order to avoid unnecessarily obscuring the invention.
- a synchronous memory write operation is requested when the CE* and WE* signals are at a logic LOW, the OE* signal is at a HIGH logic level, and an active CLK signal is provided to the synchronous control circuitry.
- the requested memory address is asserted, and the ADV* signal is LOW to indicate that the memory address is valid and should be latched by an address buffer (not shown).
- the ADV* and WE* signals can return to a HIGH logic level.
- a burst write operation can continue as long as the CE* signal is at a LOW logic level and an active CLK signal is provided to the synchronous mode detection circuit 120.
- the PULSE_SYNC pulse generated by the synchronous mode detection circuitry 120 is provided to the refresh timer 130 as well as to the OR gate 140.
- the PULSE_SYNC pulse is provided to reset the refresh timer 130 before a PULSE_OUT pulse can ever be generated by the refresh timer 130.
- the PULSE_SYNC pulse provided to the OR gate 140 by the synchronous mode detection circuitry 120 is used as the ACT_PULSE pulse to initiate a synchronous memory access operation immediately. Operation of the detection circuit 100 during a mixed mode operation will be explained with reference to the timing diagram of Figure 3.
- the timing diagram illustrates the relative timing of various signals applied to the detection circuit 100 in transitioning from an asynchronous memory read operation to a synchronous memory write operation.
- the timing diagram of Figure 3 is being provided by way of example, and should not be interpreted as limiting the scope of the present invention to a particular embodiment.
- the asynchronous memory access cycle is initiated at a time TO by providing a LOW logic level CE* signal (i.e., chip enable), asserting a memory address and strobing the ADV* signal LOW to indicate that the memory address input is valid.
- CE* i.e., chip enable
- the asynchronous mode detection circuitry 110 ( Figure 1) generates a PULSE_ASYNC pulse in response to the assertion of the memory address, which begins a time delay t d 330 of the refresh timer 130. As shown in the timing diagram of Figure 3, the time delay t d 330 is approximately 25 ns.
- a PULSE_OUT pulse is generated at a time Tl by the refresh timer 130 and provided through the OR gate 140 to the DRAM activation circuits 150 as an ACT_PULSE pulse to initiate a memory access operation in the DRAM memory core.
- the OE* signal t.e., output enable
- the OE* signal is made active by changing it to a logic LOW level at a time T2.
- valid read data 340 is provided at the input/output (IO) terminals of the memory device.
- the IO terminals are placed in a high impedance state by returning the OE* signal to a HIGH logic level, and the memory device is put in a standby state by changing the CE* signal to a HIGH logic level.
- the time T3 represents the end of the asynchronous memory access cycle.
- the transition from the asynchronous memory access mode to a synchronous memory access mode occurs on the rising edge of the CLK signal following a time T4, that is, when the CE* signal becomes active, or more specifically, when the CE* signal goes LOW.
- T4 the CE* signal becomes active at the time T4
- an asynchronous memory access operation will be executed until a rising edge of the CLK signal in combination with the ADV* signal is detected.
- the asynchronous memory access operation is cancelled, and a synchronous memory access operation is initiated instead.
- time delay t d 330 is approximately 25 ns
- a maximum time of 25 ns can elapse from the time the CE* signal becomes active at the time T4 and the time when the rising edge of the CLK signal is detected. Otherwise, the asynchronous memory access operation that is assumed to have been initiated will begin in the DRAM memory core before the synchronous memory access operation.
- the memory device is enabled by changing the logic level of the CE* signal to LOW, and a write operation is indicated by strobing the WE* signal LOW.
- a memory address is also asserted and the ADV* signal is strobed LOW to signal that the address input is valid.
- a synchronous write operation in the DRAM memory core is initiated when, in response to a rising edge of the CLK signal, the synchronous mode detection circuitry 120 ( Figure 1) detects the active CE* and WE* signals and generates a PULSE_SYNC pulse that is provided to the DRAM activation circuits 150 through the OR gate 140.
- the memory address is latched on the rising edge of the CLK signal as well.
- the ADV* and WE* are returned to a HIGH logic level, while the CE* signal remains at a LOW logic level to indicate that the requested synchronous memory write operation should not be terminated.
- the asynchronous mode detection circuitry 110 which also received the CE*, ADV*, and address signals, will generate a PULSE_ASYNC pulse.
- the PULSE_ASYNC pulse is generated in response to the CE* signal becoming active at the time T4, and an asynchronous memory access operation is started on the refresh timer 130 ( Figure 1).
- a PULSE_SYNC pulse generated by the synchronous detection circuitry 120 at a time T5 cancels the queued asynchronous memory access operation.
- the PULSE_ASYNC pulse is automatically generated in response to the assertion of the memory address.
- the refresh timer will begin the time delay. Consequently, in order to prevent a PULSE OUT pulse from being generated and interrupting the synchronous memory write operation, which as previously discussed is initiated at the time T5, the refresh timer 130 is reset and disabled by the PULSE_SYNC pulse generated by the synchronous mode detection circuitry 120. As a result, a PULSE_OUT pulse is never generated by the refresh timer 130.
- write data 360 present on the IO terminals is latched and written to the location in the DRAM memory core corresponding to the memory address latched at the time T5.
- the synchronous memory write operation will continue.
- the synchronous memory access operations can be terminated by returning the CE* signal to a HIGH logic level, and transition back to an asynchronous memory access can accomplished by disabling the CLK signal.
- FIG. 4 illustrates a portion of a memory device 500 according to an embodiment of the present invention.
- the memory device 500 is an asynchronous pseudo-static SRAM that includes a conventional DRAM memory array 502.
- the memory device 500 can be operated asynchronously or synchronously.
- the memory device 500 includes a command decoder 506 that receives memory commands through a command bus 508 which generates internal control signals within the memory device 500 to carry out various memory operations.
- the command bus 508 is also coupled to an asynclironous/synchronous detection circuit 512 that is in accordance with an embodiment of the present invention. Examples of the signals received over the command bus 508 include CE*, ADV*, OE*, and WE* signals, as previously described.
- Row and column address signals are provided to an address buffer 510 of the memory device 500 through an address bus 520, as well as to the detection circuit 512.
- the detection circuit 512 generates an ACT_PULSE pulse to initiate an access operation to the memory array 502.
- the ACT_PULSE pulse is provided to the command decoder 506 to initiate a memory access operation in Figure 5. It will be appreciated, however, that the ACT_PULSE signal can be provided to alternative or additional functional blocks of a conventional memory device without departing from the scope of the present invention.
- the row and column addresses are provided by the address buffer 510 for decoding by a row address decoder 524 and a column address decoder 528, respectively.
- Memory array read/write circuitry 530 are coupled to the array 502 to provide read data to a data output buffer 534 via a input-output data bus 540. Write data are applied to the memory array 502 through a data input buffer 544 and the memory array read/write circuitry 530.
- the command controller 506 responds to memory commands applied to the command bus 508 to perform various operations on the memory array 502. In particular, the command controller 506 is used to generate internal control signals to read data from and write data to the memory array 502.
- the data read from the memory array 502 are transferred to the output buffer 534 and provided on data input/output (IO) lines 550. In a write operation, the addressed memory cell is accessed and data provided on the IO lines 550 to the data input buffer 544 are stored in the memory array 502.
- IO data input/output
- Figure 5 is a block diagram of a computer system 600 including computer circuitry 602 that contains the memory device 500 of Figure 4.
- the computer circuitry 602 performs various computing functions, such as executing specific software to perform specific calculations or tasks, hi addition, the computer system 600 includes one or more input devices 604, such as a keyboard, coupled to the computer circuitry 602 to allow an operator to interface with the computer system.
- the computer system 600 also includes one or more output devices 606 coupled to the computer circuitry 602, such output devices typically being a display device.
- One or more data storage devices 608 are also typically coupled to the computer circuitry 602 to store data or retrieve data. Examples of storage devices 608 include hard disks and non- volatile memory.
- the computer system 600 also includes a wireless communication link 610 through which the computer circuitry can send and receive data through a wireless medium.
- the computer circuitry 602 is typically coupled to the memory device 500 through appropriate address, data, and control busses to provide for writing data to and reading data from the memory.
- the embodiment of the present invention described in Figure 1 includes a two-input OR gate 140 that provides the ACTJPULSE pulse to the DRAM activation circuits 150 to initiate a memory access operation based on either a PULSE_OUT pulse from the refresh timer 130 or a PULSE_SYNC pulse from the synchronous mode detection circuitry 120.
- the OR gate 140 will not be included, and the PULSE_OUT and PULSE_SYNC pulses will be provided to DRAM activation circuitry directly to initiate either an asynchronous memory access operation or a synchronous memory access operation, respectively.
- the embodiment of Figure 1 illustrates separate functional blocks for the asynchronous mode detection circuitry 110, synchronous mode detection circuitry 120, refresh timer 130, OR gate 140 and DRAM activation circuits 150.
- the various functional blocks may be combined into different arrangements than that shown in Figure 1, and still remain in the scope of the present invention. Accordingly, the invention is not limited except as by the appended claims.
Abstract
Description
Claims
Priority Applications (2)
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JP2006503177A JP4524759B2 (en) | 2003-02-03 | 2004-01-30 | Detection circuit for mixed asynchronous and synchronous memory operations |
EP04707003A EP1595213A4 (en) | 2003-02-03 | 2004-01-30 | Detection circuit for mixed asynchronous and synchronous memory operation |
Applications Claiming Priority (2)
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US10/357,862 | 2003-02-03 | ||
US10/357,862 US6920524B2 (en) | 2003-02-03 | 2003-02-03 | Detection circuit for mixed asynchronous and synchronous memory operation |
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WO2004070786A2 true WO2004070786A2 (en) | 2004-08-19 |
WO2004070786A3 WO2004070786A3 (en) | 2005-03-17 |
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PCT/US2004/002612 WO2004070786A2 (en) | 2003-02-03 | 2004-01-30 | Detection circuit for mixed asynchronous and synchronous memory operation |
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US (6) | US6920524B2 (en) |
EP (1) | EP1595213A4 (en) |
JP (1) | JP4524759B2 (en) |
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CN (1) | CN100492320C (en) |
WO (1) | WO2004070786A2 (en) |
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US9772969B2 (en) | 2003-02-03 | 2017-09-26 | Micron Technology, Inc. | Detection circuit for mixed asynchronous and synchronous memory operation |
US7522458B2 (en) | 2005-09-28 | 2009-04-21 | International Business Machines Corporation | Memory and method of controlling access to memory |
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US7320049B2 (en) | 2008-01-15 |
US9772969B2 (en) | 2017-09-26 |
CN1771481A (en) | 2006-05-10 |
EP1595213A2 (en) | 2005-11-16 |
JP2006517712A (en) | 2006-07-27 |
CN100492320C (en) | 2009-05-27 |
KR100989287B1 (en) | 2010-10-22 |
US20050207254A1 (en) | 2005-09-22 |
KR20050096177A (en) | 2005-10-05 |
US20070174575A1 (en) | 2007-07-26 |
WO2004070786A3 (en) | 2005-03-17 |
JP4524759B2 (en) | 2010-08-18 |
EP1595213A4 (en) | 2010-09-08 |
US20040153602A1 (en) | 2004-08-05 |
US20120072682A1 (en) | 2012-03-22 |
US6920524B2 (en) | 2005-07-19 |
US20100088483A1 (en) | 2010-04-08 |
US20060136692A1 (en) | 2006-06-22 |
US7506126B2 (en) | 2009-03-17 |
US7640413B2 (en) | 2009-12-29 |
US8082413B2 (en) | 2011-12-20 |
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