Patent Grant
7202545
This application claims priority to German Patent Application 103 39 787.6, which was filed Aug. 28, 2003 and is incorporated herein by reference.
The present invention relates generally to a memory module, and more particularly to a system and method for operating a memory module having an electronic printed circuit board and a plurality of semiconductor memory chips.
A memory module is a system, typically on a single circuit board, that includes a number of memory chips. Memory modules are often configured to include data lines that are divided so that any one or group of ones of data lines will access the memory chips, such as DRAMs (dynamic random access memory), individually for transferring memory data. The module can also include further lines, called first lines hereinafter, that simultaneously access all the semiconductor memory chips and, therefore, connect the latter to one another in parallel. Such first lines are, by way of example, address lines for communicating memory addresses and also control lines for communicating control commands such as reading, writing, activation or deactivation of memory cells.
On account of the parallel interconnection, each semiconductor memory chip receives the same command sequence. Only the memory contents that are communicated via the data lines leading to in each case only a single semiconductor memory chip are transferred in chip-specific fashion.
If an individual memory chip is intended to be selectively addressed, for example in order to read chip-specific data, conventionally the normal memory operation is interrupted and a special operating mode of the memory module is set, in which, for instance, chip-specific data such as test results of a chip test or the former position of the memory chip within a wafer or the batch number of the wafer that was processed in order to fabricate the memory chip are transferred. Such information is still of importance even after start-up of a memory module, in order, in the event of error clusters, to identify the identity of the error-susceptible semiconductor chips affected during fabrication in semiconductor memory chips of a multiplicity of produced memory modules. Such data are usually stored in the form of electrically one-time blowable fuses on each semiconductor chip and can later be retrieved at any point in time, but not during the normal operation of a memory module. One reason for this is that the control lines required for transferring such individual chip data, during the operation of a memory module, are already required for communicating control commands such as writing, reading, etc., or for transferring commands such as chip select, row address strobe, column address strobe, write enable, clock or clock enable and are not available for further operations. Any interrogation of chip-specific data would thus result in an interruption of the module operation.
Module-specific data containing chip-specific data can also be stored on a customary EEPROM (electrically erasable programmable read only memory) present in the memory module. However, the capacity thereof is often limited. Moreover, its content is predetermined from the outset for each repeated instance of starting operation. By way of example, the number of semiconductor memory chips and their memory capacity are stored in the EEPROM. This chip is not suitable for storing or retrieving more extensive, in particular variable, data.
Chip-specific data consequently have to be stored or retrieved via the first lines that are required during the normal operation of the memory module.
There are principally two types of memory modules that are customary, which differ with regard to their driving when a plurality of memory modules are used in memory slots of a superordinate memory unit. In a memory arrangement whose main board has a plurality of module slots fitted with memory modules, each semiconductor memory chip of each memory module must be addressable selectively with respect to the rest of the semiconductor memory chips, at least in order to write or read memory data during normal memory operation.
In the case of SDRAMs (synchronous dynamic random access memory), the memory chips of a single memory module are in each case connected in parallel, so that all the memory chips are in each case accessed simultaneously. For the selection of a specific memory module or module slot (or a specific module side in the case of two-bank modules), use is made of a signal “chip select” on the main board, as a result of which in each case all the memory chips of a specific memory module are driven simultaneously. The data exchange is effected synchronously, i.e., at regular time intervals that are oriented to the clock signal and amount to a multiple of the clock cycle time. In the event of all the memory chips of the memory module being accessed in parallel, the bus width of the module results from the bus width of a memory chip times the number of memory chips connected in parallel, in which case in some instances an additional semiconductor memory chip is additionally connected in parallel for the purpose of error correction. A distinction is made between SDR-SDRAMs (single data rate) and DDR-SDRAMs (double data rate) depending on whether only the rising or both the rising and the falling clock edges of the clock signal are utilized for data transfer.
On the main board, the memory modules are likewise connected in parallel with one another. The signal “chip select” serves for driving a specific memory module, as a result of which the data bus of in each case a single memory module is selected. The chip select signal limits the parallelism of the driving; as a result, all the memory chips of only a single memory module are driven in parallel with one another.
In the case of SDRAMs, the abovementioned chip-specific driving is not possible at least during the normal memory operation. This is already unsuccessful due to the module-internal connection in parallel of all the semiconductor memory chips.
The memory modules of the other design are called RDRAMs, named after the provider Rambus. In the case of the Rambus system, a plurality of memory modules that are inserted into module slots of a main board are connected in series. During the so-called initialization of a memory module or the totality of a plurality of memory modules, each memory chip receives a chip-specific memory identifier. This daisy chain initialization enables a direct driving of a specific memory chip. In this case, too, the memory chips of a memory module are connected in parallel with one another. Use is made of a data bus that has 16 data lines, for example, and is rather narrow in comparison with SDRAMs. For example, the data bus transports data blocks within 4 clock times (in a “burst 8 mode” in the case of DDR-SDRAMs). During the operation of an RDRAM, the data sent to a memory module are simultaneously transported to all the memory chips of the module. However, the processing or taking-up of the data occurs only in the addressed memory chip. The rest of the memory chips “eavesdrop” in this time but do not react actively.
Thus, in the case of RDRAMs, the chip-specific driving is effected via the control lines, to be precise exclusively for the purpose of storing and interrogating memory data. If the intention is additionally to interrogate chip-specific data, for instance test data of previous memory tests, the normal operation has to be interrupted. Furthermore, there is the major disadvantage that when a specific memory chip is being driven, the rest of the memory chips of the same module are paralyzed since they cannot be driven simultaneously via the same data bus of the memory module. In the case where a plurality of RDRAMs are cascaded on a main board, the further disadvantage arises that empty module slots that are not occupied have to be occupied by bridging modules because otherwise the temporal coordination of the data exchange collapses.
In one aspect, the invention relates to a memory module having an electronic printed circuit board and having a plurality of semiconductor memory chips, lines that can be driven electrically via first external contacts of the printed circuit board branching toward the semiconductor chips and thereby connecting the semiconductor chips in parallel with one another. The invention furthermore relates to a method for operating a memory module.
The preferred embodiment of the present invention provides a memory module, as well as a method for operating a memory module, in which it is possible to selectively drive individual semiconductor memory chips without interrupting the normal memory operation. For example, an individual chip can be selected while another is being interrogated chip-specific information that is not regularly required. Furthermore, in preferred embodiments, a new type of data transport is enabled within a memory module and also within an arrangement of a plurality of memory modules, in the case of which a plurality of semiconductor memory chips can be addressed in turn. The intention is for this progressive addressing of a plurality of semiconductor memory chips to be made possible in particular by means of a single, one-time instruction.
With regard to the memory module, this object is achieved according to the invention by virtue of the fact that a first connecting line, which can be driven electrically via a second external contact of the printed circuit board and leads to a first semiconductor memory chip, and a second connecting line, which can be read out via a third external contact of the printed circuit board and leads to a last semiconductor memory chip, and also at least one connection line leading from one respective semiconductor memory chip to another respective semiconductor memory chip are provided, the semiconductor memory chips being connected by the two connecting lines and by the at least one connection line to form a series circuit between the second and the third external contact of the printed circuit board.
According to one aspect of the invention, an electrical loop into which all the semiconductor memory chips are interposed is provided between two external contacts of the printed circuit board of a memory module. Connection lines lead from one respective semiconductor memory chip to the next; consequently, a direct connection or branching-off from these intermediate lines to an external contact does not exist. Such an interconnection is not customary in memory modules in which all the memory chips are jointly connected to the same external contacts of the printed circuit board via lines that branch like a phylogenetic tree.
In view of the equivalence of the semiconductor memory chips among one another, it initially appears to be absurd to connect two of the semiconductor memory chips, i.e., a first and a last, directly to electrical external contacts, while the rest of the semiconductor memory chips have lines that only lead to adjacent memory chips but have no connection to any external contact. According to the preferred embodiment, however, the series circuit formed with the aid of the connection lines described above is interposed as an electrical loop between two external contacts of the printed circuit board.
Such an electrical loop that traverses one semiconductor memory chip after the other starting from an external contact or from a buffer chip connected thereto on the printed circuit board and at the end returns again to a further external contact or buffer chip does not correspond to the principle—familiar from customary module printed circuit boards—of permitting a line proceeding from an external contact to end at one semiconductor memory chip (as in the case of data lines) or, in the case of branching like a phylogenetic tree, at a plurality or all of the semiconductor memory chips (as in the case of address lines or control lines). Both SDRAM and RDRAM printed circuit boards have a phylogenetic tree-like or comb-like interconnection of all the memory chips which are in each case situated at the line ends.
According to the preferred embodiment of the present invention, by contrast, the above-mentioned interconnection, which represents a loop drawn through the memory module, is utilized for a new type of memory driving. Although the electrical loop that traverses all the memory chips in turn without preferring a specific memory chip does not appear a priori to enable a chip-selective driving of individual memory chips, it is entirely possible, according to the invention, for specific memory modules to be driven selectively when the data that pass via the electrical loop or in some other way to the memory chips contain memory-module-specific information. Even if each memory chip processes the data obtained via the electrical loop, the way in which this processing occurs can be influenced in a chip-specific manner with the aid of the data themselves or with the aid of some other driving of individual memory chips. This makes it possible that, within the chain of memory chips, an individual memory chip processes the data obtained via the electrical loop differently than the rest of the memory chips, so that, at the end of the chain, a data signal specific to the relevant memory chip is output to the external contact at the end of the electrical loop. This chip-specific data signal can therefore be assigned to the relevant memory chip and transport chip-specific information without disturbing the conventional parallel operation on the memory module. In this way, both SDRAM and RDRAM memory modules can be equipped for retrieving chip-specific additional information at any time.
A preferred embodiment provides for the series circuit to be formed in such a way that data sent to the first semiconductor memory chip via the second external contact are forwarded in temporally offset fashion via the connection lines to the respective next semiconductor memory chip of the series circuit. In this case, the electrical loop between the second and third external contacts is exclusively set up for unidirectional data transport; the data that have been originally input or have been altered by one of the memory chips are forwarded via the connection lines to the next memory chip in temporally offset fashion. The temporal offset between the data transport of two connection lines connected to the same memory chip is preferably chosen to be very large in comparison with the clock cycle time, in order to enable even complex interrogations, for example of extensive test data, in the memory chips.
It is preferably provided that a third connecting line, which can be driven via a fourth external contact of the printed circuit board and connects the semiconductor memory chips in parallel with one another, is provided, by means of which the semiconductor memory chips can be activated with the aid of individual memory identifiers in each case individually selectively with respect to further semiconductor memory chips. In this case, the selection of a specific memory chip is not effected with the aid of the data communicated via the electrical loop, but rather with the aid of an additional selection signal that is sent to all the semiconductor memory chips but addresses only one memory chip on account of its chip-specific identifier. As a result, in the chip, a processing process is activated that leads to the outputting, inputting or transformation of the desired chip-specific information.
It is preferably provided that exclusively those semiconductor memory chips which are selectively activated with the aid of the third connecting line are caused to alter or to supplement data received via the series circuit prior to a forwarding to the respective next semiconductor memory chip. In the case of this embodiment, the non-selected memory chips are configured in such a way that they only serve for the temporally offset forwarding of the data flowing via the electrical loop, without changing the data themselves, at least not with regard to their relevant content. By contrast, the selected memory chip processes the incoming data and forwards changed data, preferably supplemented by a chip-specific data addition, to the connection lines to the next semiconductor memory chip. These information items are read out via the third external contact and evaluated on a main board.
It is preferably provided that the memory module is formed in such a way that, in the event of a start-up of the memory module, each semiconductor memory chip of the series circuit is assigned an individual memory identifier corresponding to a consecutive number of the respective semiconductor memory chip within the series circuit. In the case of this particular embodiment, not just one but each semiconductor memory chip is caused to alter or to supplement the data arriving at the chip via the respective connection line. In this case, the number of changes or supplementations may be used to convey to the main board information about the total number of connected memory chips of one or a plurality of memory modules. Equally, this embodiment may be used to assign to each memory chip a chip-specific memory identifier, which can later be used after commissioning of the memory module for chip-selective driving. These types of initialization have the advantage over memory identifiers that are burned into the chips with the aid of laser fuses or electrical fuses that, upon each commissioning of the memory module, can be established and assigned anew and be automatically adapted in the case of changes in the meantime to the fitting of the memory module with memory chips or of a main board with memory modules.
It is preferably provided that the memory module is formed in such a way that, in the event of each start-up of the memory module, each semiconductor memory chip that receives, via the series circuit, a memory identifier corresponding to its consecutive number within the series circuit outputs to the connection line to the respective next semiconductor memory chip or to the second connecting line a memory identifier corresponding to the next higher consecutive number of a semiconductor memory chip. The signal output to the third external contact at the end of the series circuit thus directly reproduces the total number of memory chips used or, as an alternative thereto, a quantitative indication of the total available memory capacity.
It is preferably provided that the lines that can be driven via the first external contacts are address lines and control lines. Memory addresses in all the semiconductor memory chips are addressed simultaneously with the aid of the address lines; the control lines serve for communicating write, read and further commands.
The semiconductor memory chips preferably contain volatile random access memories, in particular DRAMs.
Finally, it is provided that the first external contacts and the second and the third external contacts are arranged in a common contact strip of the printed circuit board.
A memory module according to embodiments of the invention is likewise used to develop a memory module arrangement having a main board having a plurality of module slots, a memory module according to one of the embodiments described above being connected to one or to a plurality of module slots, and each module slot having two contacts for connecting a series circuit of semiconductor memory chips on both sides.
The memory module according to the invention enables a novel interconnection of a plurality of memory module slots of a main board; on account of the series circuits that in each case traverse a memory module in loop-type fashion, series circuits of all the semiconductor memory chips of all the module slots can be formed with the aid of the, in each case, two contacts per module slot. The resultant overall chain of memory chips is suitable for counting up and individually identifying all the memory chips in accordance with their total number on the main board; as a result, even after a rearrangement or exchange of memory modules, the main board recognizes each change with regard to the number or the memory capacity of the memory chips and thereby enables remote access controls which manage without actively instigated parameter changes.
One embodiment provides for the main board to be constructed in such a way that the semiconductor memory chips of all the memory modules connected to the module slots are connected to form a single series circuit via the two respective contacts of the module slots. In this case, connection lines of the main board connect two contacts of mutually adjacent module slots.
A further embodiment provides for the main board to be constructed in such a way that, with the aid of a module identifier, a respective series circuit of semiconductor memory chips of a memory module can be driven selectively with respect to series circuits of semiconductor memory chips of further memory modules. In this case, the memory modules or module slots are connected in parallel with one another and are selectively driven with the aid of a chip select signal. The further selection—not possible during operation in the case of conventional memory modules—with regard to an individual semiconductor memory chip is effected with the aid of the above-described series circuit traversing the memory module in loop-type fashion.
Aspects of the invention furthermore relate to a method for operating a memory module having a series circuit having a plurality of semiconductor memory chips that are connected in series on a printed circuit board between two external contacts of the printed circuit board. According to the invention, data are conducted via one of the two external contacts to a first semiconductor memory chip and via connection lines in each case in temporally offset fashion from one semiconductor chip to a next semiconductor chip and from a last semiconductor memory chip to the second of the two external contacts. By virtue of this type of data transport through all the semiconductor memory chips back to an external contact again, it is possible to implement the electrical loop for progressively transferring data provided to the respective next semiconductor memory chip and—in the case of a selected semiconductor chip—with the data being altered. In this case, the data transport is effected from the first to the last semiconductor memory chip without a feedback of the memory chips arranged in the center of the series circuit to one of the external contacts of the printed circuit board, by means of which the semiconductor memory chips are conventionally driven in the case of SDRAMs and also RDRAMs; the exclusive forwarding of data, if appropriate after the latter have been changed or supplemented, via connection lines between, in each case, two memory chips without any feedback with a main board makes it possible to utilize a new type of data transport for memory modules.
In a preferred type of embodiment, it is provided that with the aid of an individual memory identifier, an individual semiconductor memory chip is caused, selectively with respect to the rest of the semiconductor memory chips to alter or to supplement data received via the series circuit prior to the forwarding to the respective next semiconductor memory chip.
It is preferably provided that in the event of start-up of the memory module, each of the semiconductor memory chips connected in series is assigned an individual memory identifier corresponding to a consecutive number of the respective memory chip within the series circuit, the memory identifiers being retained only during the operation of the memory module. The erasure of the assigned memory identifiers when the memory module or a main board is switched off has the advantage that, even after a rearrangement or alteration of memory modules in module slots of a main board, upon later turn-on, the electrical loops through the memory modules together reproduce the changed memory configuration in the form of altered memory identifiers, without this necessitating an intervention externally, for example an active parameter adaptation.
It is preferably provided that with the aid of the series circuits, information items are read selectively from a semiconductor memory chip or are written thereto by virtue of the memory chip being instructed with the aid of its memory identifier, as the only one of the semiconductor memory chips connected in series, to alter or to supplement data that are conducted from the first of the two external contacts via the semiconductor memory chips to the second of the two external contacts. The rest of the memory chips in this case serve only for the time-delayed forwarding of the data, but without changing them. Unlike in RDRAM memory modules, the time delay is not prescribed by external conditions.
The invention is explained below with reference to
According to the preferred embodiment, the memory module 1 has a series circuit of semiconductor memory chips 3 that are electrically connected between a second external contact 4 and a third external contact 5 of the printed circuit board 2 (or between buffer memories or buffer chips connected to the external contacts) and thus form an electrical loop. Along the electrical loop, data D0 can be conducted from the second external contact 4 to a first semiconductor memory chip 3a, from the latter via connection lines 18 to further, respectively next connected semiconductor memory chips 3b, 3c, . . . , and finally to a last semiconductor memory chip 3n, from which they can be fed via a second connecting line 15 and the third external contact 5 to a main board to which the memory module 1 can be connected. The first and second connecting lines 14 and 15 are equivalent to one another, in which case, when the circuit is operated unidirectionally, one lead 14 represents an input line and the other lead 15 represents an output line of the memory module. In between, in the direction of the arrows illustrated, data D0 are transported along the chain of memory chips 3, individual memory chips 3b that are selected selectively with respect to the rest of the memory chips 3a, 3c, . . . 3n, for example with the aid of a chip-specific memory identifier Q2, being caused to change or to supplement the received data D0 and to forward the changed or supplemented data D2 to the downstream chain of connected memory chips 3c, . . . , 3n. The non-selected memory chips 3a, 3c, . . . , 3n, which do not react to the chip-specific memory identifier Q2 respectively selected, do not alter the contents of the data D2 provided via the connection lines 18, so that chip-specific information and also that chip to which they are assigned can be read from the data that can be read out at the third external contact 5.
The chip-specific memory identifier Q2 may be provided either via the electrical series circuit between the external contacts 4, 5 or via an additional line 19 that drives the semiconductor memories in parallel. In the addressed memory chip 3b, a process P is activated which ensures that the data D0 received via the electrical loop are not simply forwarded, but rather are processed, i.e., stored, utilized for forwarding further information D2 or converted or supplemented. In both cases, the selective driving of a specific semiconductor memory chip 3b is not effected via the parallel-branched control lines 17 or address lines 16 that are always fully utilized during normal memory operation. Consequently, the memory operation need not be interrupted in order in the meantime to interrogate additional information, for instance test data or other chip-specific information.
The electrical loop between the external contacts 4, 5 primarily enables arbitrary data to be passed on from a respective semiconductor memory chip 3 to a next chip in an ordered sequence, it being possible, in principle, to read out tabular accumulations of chip-specific data of all the semiconductor memory chips 3 or else to a carry out computation operations dependent on the total number of semiconductor memory chips 3, such as, for instance, an initialization based on the position of a semiconductor memory within the series circuit. The information output by all the semiconductor memory chips 3 requires only a single output line 15, which, just like the input line 4, requires only a single external contact 5 in the contact strip 8. Even though in reality the leads 14, 15 and the connection lines 18 are embodied as a line bus in each case having a plurality of lines running parallel to one another, the electrical loop with series-connected semiconductor memory chips 3 that is used according to the invention manages with an extremely small number of additional external contacts.
Such a series circuit R can be used according to the invention to assign to each semiconductor memory chip an individual memory identifier corresponding to its consecutive number. For this purpose, in accordance with
A few optional steps LP, LA and J then follow, which, however, may in each case be circumvented individually and independently of one another, as indicated by detours represented on the right and left of these steps on the basis of
The entire data sequence illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 39 787 | Aug 2003 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5243703 | Farmwald et al. | Sep 1993 | A |
| 5357621 | Cox | Oct 1994 | A |
| 5859809 | Kim | Jan 1999 | A |
| 6144576 | Leddige et al. | Nov 2000 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20050098881 A1 | May 2005 | US |
