Encoding data in a modified-memory system

Abstract

Implementations of Data Bus Inversion (DBI) techniques within a memory system are disclosed. In one embodiment, a set of random access memory (RAM) integrated circuits (ICs) is separated from a logic system by a bus. The logic system can contain many of the logic functions traditionally performed on conventional RAM ICs, and accordingly the RAM ICs can be modified to not include such logic functions. The logic system, which can be a logic integrated circuit intervening between the modified RAM ICs and a traditional memory controller, additionally contains DBI encoding and decoding circuitry. In such a system, data is DBI encoded and at least one DBI bit issued when writing to the modified RAM ICs. The RAM ICs in turn store the DBI bit(s) with the encoded data. When the encoded data is read from the modified RAM ICs, it is transmitted across the bus in its encoded state along with the DBI bit(s). The logic integrated circuit then decodes the data using the DBI bit(s) to return it to its original state.

Claims

1. A system to transmit data, the system comprising: a logic system including encoding circuitry to receive sequentially groups of N original data bits from a memory controller, the encoding circuitry to encode selectively each group of the N original data bits to form a corresponding group of N encoded data bits, and to generate at least one encoding indicator associated with each group of the N encoded data bits; and at least one memory structure separate from the logic system and having one or more hardware-modified memory devices, wherein the one or more hardware-modified memory devices do not contain encoding circuitry, the logic system being configured to intervene between the memory controller and the at least one memory structure.

2. The system of claim 1, wherein the logic system includes at least one of a data bit inversion (DBI) encoder and a DBI decoder.

3. The system of claim 1, wherein a portion of the at least one memory structure is configured to provide storage for a data bit inversion (DBI) indicator.

4. The system of claim 1, wherein the logic system includes a data bit inversion (DBI) encoder and DBI decoding is to be performed exclusively by the one or more hardware-modified memory devices.

5. A method, comprising: sequentially receiving groups of N original data bits at a logic device, the logic device having circuitry to implement one or more logic functions including an encoder, the logic device further having at least one circuit selectable from a group of circuits consisting of command decoder, for interpreting a write command and enabling the encoder, and queuing circuitry for a plurality of memory devices, redundancy circuitry for determining faulty memory addresses in the plurality of memory devices and rerouting around such faulty addresses to functioning ones of the plurality of memory devices, and address decode circuitry for the plurality of memory devices; selectively encoding each of the groups of N original data bits at the logic device to form groups of N encoded data bits and at least one encoding indicator associated with each of the groups of N encoded data bits; and transmitting the groups of N encoded data bits and their associated at least one encoding indicator for storage in selected ones of the plurality of memory devices, the plurality of memory devices being fabricated on a structure separate from the logic device, the plurality of memory devices not containing the at least one circuit or the encoder that are present on the logic device.

6. The method of claim 5, wherein the at least one encoding indicator is a data bit inversion (DBI) indicator.

7. The method of claim 5, further comprising selectively decoding the groups of N encoded data bits in accordance with their associated at least one encoding indicator at the at least one memory device to recover each of the groups of N original data bits.

8. The method of claim 5, further comprising retrieving at least a portion of the selectively decoded ones of the groups of N encoded data bits only without retrieving the associated at least one encoding indicator from selected ones of the plurality of memory devices.

9. The method of claim 5, wherein the selectively encoding each of the groups of N original data bits comprises selectively inverting at least some of the N original data bits in each group in accordance with an algorithm to form the groups of N encoded data bits.

10. The method of claim 5, further comprising retrieving at least a portion of the groups of N encoded data bits in their encoded state and their associated at least one encoding indicator from the at least one memory device.

11. A method of transmitting data, the method comprising: sequentially receiving groups of N original data bits at a logic integrated circuit, the logic integrated circuit having circuitry to implement one or more logic functions including an encoder, the logic device further having at least one circuit selectable from a group of circuits consisting of command decoder, for interpreting a write command and enabling the encoder, and queuing circuitry for at least one memory device and address decode circuitry for the at least one memory device; selectively encoding each of the groups of N original data bits at the logic integrated circuit to form groups of N encoded data bits and at least one encoding indicator associated with each of the groups of N encoded data bits; transmitting the groups of N encoded data bits and their associated at least one encoding indicator to the at least one memory device by way of a bus; selectively decoding the groups of N encoded data bits in accordance with their associated at least one encoding indicator at the at least one memory device to recover each of the groups of N original data bits, the at least one memory device being fabricated on a structure separate from the logic device, the at least one memory device further being fabricated without a data bit inversion (DBI) encoder and not containing the at least one circuit or the encoder that are present on the logic device; and storing the recovered groups of N original data bits in the at least one memory device.

12. The method of claim 11, further comprising transmitting the recovered groups of N original data bits read from the at least one memory device to the logic integrated circuit by the bus.

13. A system to transmit data, the system comprising: a logic system including encoding circuitry to receive sequentially groups of N original data bits from a memory controller, the encoding circuitry to encode selectively each group of the N original data bits to form a corresponding group of N encoded data bits, and to generate at least one encoding indicator associated with each group of the N encoded data bits, the logic system further including at least one circuit selectable from a group of circuits consisting of command decoder, to interpret a write command and enable the encoding circuitry, and queuing circuitry for a plurality of hardware-modified memory devices, redundancy circuitry to determine faulty memory addresses in the plurality of hardware-modified memory devices and to reroute around such faulty addresses to functioning ones of the plurality of hardware-modified memory devices, and address decode circuitry for the plurality of hardware-modified memory devices; and at least one memory structure separate from the logic system and having the plurality of hardware-modified memory devices, the at least one memory structure and the plurality of hardware-modified memory devices not containing the at least one circuit or the encoder that are present on the logic system, the logic system being configured to intervene between the memory controller and the at least one memory structure.

14. The system of claim 13, further comprising the memory controller to transmit the groups of N original data bits to the logic system, the memory controller being separate from the logic system.

15. The system of claim 13, wherein neither the at least one memory structure nor the plurality of hardware-modified memory devices contain redundancy circuitry.

16. The system of claim 13, wherein the logic system further comprises test mode circuitry.

17. The system of claim 13, wherein the plurality of hardware-modified memory devices includes a decoder to receive sequentially each group of the N encoded data bits and their associated at least one encoding indicator from the logic system, the decoder being operatively arranged to decode selectively each group of the N encoded data bits in accordance with their at least one encoding indicator to recover each group of the N original data bits, the at least one memory structure is further to store each of the recovered groups of the N original data bits.

18. The system of claim 13, wherein the encoding circuitry is to encode selectively each group of the N original data bits using an algorithm to selectively invert at least some of the N original data bits in each group to form the groups of the N encoded data bits.

19. The system of claim 18, wherein the algorithm is to reduce transitions between sequential groups of the N encoded data bits.

20. The system of claim 19, wherein the logic system and the at least one memory structure are vertically stacked in the module.

21. The system of claim 18, wherein the algorithm is to reduce an occurrence frequency of a given binary logic state in each of the groups of N encoded data bits.

22. The system of claim 18, wherein the algorithm is to balance logic states of each group of the N encoded data bits.

23. The system of claim 18, wherein the algorithm is a data bit inversion (DBI) algorithm.

24. The system of claim 13, wherein the logic system comprises a logic integrated circuit.

25. The system of claim 13, wherein the logic system and the at least one memory structure are packaged in a module.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a block diagram of a data transmission system.

(2) FIGS. 2A and 2B illustrates a block diagram and a data table illustrating a minimum transitions DBI technique.

(3) FIG. 3A illustrates a system in which modified RAM ICs are used in conjunction with a logic integrated circuit having circuitry implementing functions traditionally present on RAM ICs.

(4) FIG. 3B illustrates a system, like that depicted in FIG. 3A, in which the logic integrated circuit also decodes the addresses for the modified RAM ICs.

(5) FIG. 4 illustrates how the systems of FIGS. 3A and 3B can be implemented using a vertically-stacked memory module on a printed circuit board.

(6) FIGS. 5 and 6 illustrate an embodiment of the invention in which DBI encoding and decoding is included on the logic integrated circuit, and in which the modified RAM ICs include a storage area for DBI bits.

(7) FIGS. 7A and 7B illustrate a system, similar to that of FIGS. 5 and 6, in which a modified RAM IC is dedicate to providing DBI storage.

(8) FIGS. 8A-8C illustrate another embodiment of the invention in which DBI encoding is included on the logic integrated circuit, but DBI decoding is included on the modified RAM ICs, allowing for one-way DBI implementation but obviating the need to store DBI bits within the modified RAM ICs.

DETAILED DESCRIPTION

(9) Implementations of Data Bus Inversion (DBI) techniques within a memory system are disclosed. In one embodiment, a set of random access memory (RAM) integrated circuits (ICs) is separated from a logic system by a bus. The logic system can contain many of the logic functions traditionally performed on conventional RAM ICs, and accordingly the RAM ICs can be modified to not include such logic functions. The logic system, which can be a logic integrated circuit intervening between the modified RAM ICs and a traditional memory controller, additionally contains DBI encoding and decoding circuitry. In such a system, data is DBI encoded and at least one DBI bit issued when writing to the modified RAM ICs. The RAM ICs in turn store the DBI bit(s) with the encoded data. When the encoded data is read from the modified RAM ICs, it is transmitted across the bus in its encoded state along with the DBI bit(s). The logic integrated circuit then decodes the data using the DBI bit(s) to return it to its original state.

(10) In another embodiment, DBI may be implemented only for data being transmitted in one direction over the bus, for example, when writing to the memory. In this implementation, the logic integrated circuit includes a DBI encoder, with the DBI decoder occurring on the modified RAM ICs. Data written to the modified RAM ICs is encoded and issued with at least one DBI bit on the bus. At the modified RAM ICs, the data is then decoded using the DBI bit(s) and stored in its original un-encoded state. When data is read from the modified RAM ICs, no DBI encoding occurs, and there is no need to have stored the DBI bit(s) in the modified RAM ICs.

(11) A system 100 benefiting from the implementation of DBI is shown in FIG. 3A. System 100 comprises a system for reading/writing from/to a memory set 25, which in the illustrated example comprises modified RAM ICs 16.sub.x, whose modification from otherwise standard RAM ICs is discussed further below. In such a system, it can be assumed, for illustrative purposes, that a microprocessor 10 reads from and writes to the memory set 25, but this is merely one example, and any other device or system could be used to so query the memory. In one embodiment, the modified RAM ICs 16.sub.x in the memory set 25 comprise dynamic RAM (DRAM) arrays of cells 61, but could also comprise static RAM (SRAM) cells, or various other types of write/erasable non-volatile memory (e.g., NAND Flash cells, Flash EPROM cells, etc.).

(12) Intervening between the microprocessor 10 and the memory set 25 is a memory controller 12. Memory controllers 12 are well known in the art and work to create a standard interface 20 with which the microprocessor 10 can predictably communicate. The memory controller 12 couples to the microprocessor's data (DQ), address (A), and control (cntl) busses 11, and converts them to new busses 13 DQ, A, and cntl suitable for interfacing with a logic integrated circuit (IC) 14, discussed further below. Memory controller 12 typically comprises an integrated circuit separate and independent from other components in the system 100, but this is not strictly necessary, and the controller 12 could be integrated with other components if desired. The memory controller 12 can comprise any well known memory controller 12 used in the industry.

(13) In the disclosed embodiment, a logic IC 14 intervenes between the memory controller 12 and the modified RAM ICs 16.sub.x, and in this respect both the logic IC 14 and the modified RAM ICs 16.sub.x differ from standard memory typically used. Departing from such standard solutions, the logic IC 14 contains much if not all of the logic circuitry 49 typically present on a standard RAM IC (not shown). For example, the logic IC 14 can contain command decode and queuing circuitry 50. Such circuitry 50 interprets the various command signals on the cntl data bus (such as signals write enable (WE), row address strobe (RAS), column address strobe (CAS), and chip select (CS), assuming the modified RAM arrays 16.sub.x comprise DRAM memory), and issues and organizes the commands as appropriate for distribution to the modified RAM ICs 16.sub.x along a control bus cntl intervening between the logic IC 14 and the RAM ICs 16.sub.x. The logic IC 14 may also contain redundancy circuitry 52 for determining faulty memory addresses in the modified RAM ICs 16.sub.x and for rerouting around such defective addresses to functioning memory cells using programmable fuses or antifuses, as is well known. Logic IC 14 may additionally contain error correction circuitry 54, which can comprise well known circuitry for assessing and correcting faulty data in accordance with any number of error correction algorithms. Further, logic IC 14 may contain test mode circuitry 56, which is typically used during manufacturing and/or under the application of special test commands to test the operation of the various modified RAM ICs 16.sub.x. Typically, such circuits 50-56 are formed as part of the peripheral logic of a standard memory integrated circuit (not shown), but in the illustrated system such circuitry has been removed from the modified RAM ICs 16.sub.x.

(14) Logic IC 14 may also contain additional integration circuitry 58 not traditionally contained on a conventional RAM ICs, but which are relevant more globally to the modular integration of a number of memory arrays. For example, integration circuitry 58 can assess the operation of the various signals on bus 15 (DQ, A, end) intervening between the logic IC 14 and the modified RAM ICs, and if necessary can reroute around any connections deemed to be faulty.

(15) As a result of circuits 50-58 being present on the logic IC 14, the modified RAM ICs 16.sub.x need not contain such circuits, and instead modified. RAM ICs 16.sub.x can comprise only the array of storage cells 61 and other minimal circuitry desirable for the functioning of such cells. Such other minimal circuitry can comprise the sense amplifiers 62 used to sense the data state of the cells, column decoder circuitry 64, row decoder circuitry 66, column driver circuitry 68, and row driver circuitry 70.

(16) By moving the logic circuitry 49 off of the modified RAM ICs 16.sub.x, the RAM ICs 16.sub.x, can be made smaller in area. Reducing the size of the RAM ICs 16.sub.x helps the yield and reliability of such devices, and allows their assembly into a smaller package or packages, as discussed further below with reference to FIG. 4.

(17) Because the logic circuitry 49 is moved off of the RAM ICs 16.sub.x and onto the logic IC 14, a bus 15 intervenes between the logic IC 14 and the modified RAM ICs 16.sub.x, as mentioned above. Bus 15 contains data (DQ), address (A), and control (cntl) signals that might otherwise appear internally on a standard RAM IC.

(18) FIG. 3B illustrates a modification to the system 100 in which the address decode circuitry (e.g., column and row decoders 64 and 66) has been moved off of the modified RAM ICs 16.sub.x and onto the logic IC 14. Specifically, a new address decode block 75 is included which performs column and row decoding, and (in the illustrated example) decoding to choose an appropriate one of the modified RAM ICs 16.sub.x. Accordingly, in this embodiment, bus 15 contains the already-decoded row and column driver signals (Cx.sub.i; Ry.sub.i) necessary to access any of the x columns and y rows of the various modified RAM ICs 16.sub.x. As shown, the column and row driver circuits 68 and 70 still remain on the modified RAM ICs 16.sub.x, along with the sense amplifiers 62, but these circuit blocks could also be moved onto the logic IC 14 in an alternative embodiment, making the modified RAM ICs smaller still. While FIG. 3B illustrates a full decoding of the addresses on bus A, note that this is not strictly required and instead some or all of the address decoding could occur on the modified. RAM ICs 16.sub.x.

(19) FIG. 4 shows portions of the systems 100 or 100 of FIGS. 3A and 3B as they could be manufactured. As shown, a standard memory controller 12 is affixed to a printed circuit board (PCB) 30 using solder bumps 80 as is typical. Some of these bumps 80 will correspond to signals on bus 11 between the memory controller 12 and the microprocessor 10 (not shown in FIG. 4), while other bumps will correspond to signals on bus 13 between the memory controller 12 and the logic IC 14.

(20) In the implementation shown in FIG. 4, the logic IC 14 and the modified RAM ICs 16.sub.x are integrated in a multichip module 40. As shown, the logic IC 14 and the modified RAM ICs 16.sub.x are vertically stacked in the module 40 within a singular package. To facilitate the running of the signals on bus 15, through-silicon vias (TSVs) 83 run though the logic IC 14 and the modified RAM ICs 16.sub.x. The module 40 is also affixed to the printed circuit board using solder bumps 82.

(21) Although shown with the memory controller 12 and module 40 on the same PCB 30, this is not strictly necessary. Additionally, the microprocessor 10 (not shown) could be on the same or separate PCBs from the memory controller 12 and/or the module 40. Further, any combination of the microprocessor 10, memory controller 12, and module 40 could be integrated within its own package or multichip module. Additionally, it is possible that the functionality contained within the memory controller 12 might also be moved to the logic IC 14, thus eliminating the need for the memory controller 12 and the bus 13 in the system. Thus, the assembled configuration shown in FIG. 4 is merely one example of how system 100 or 100 could be implemented.

(22) With embodiments of basic systems described, discussion now turns to the application of Data Bus Inversion (DBI) to such systems. As shown in FIG. 5, system 200 has had its logic IC 14 modified to include a DBI encoder/decoder 210. The DBI encoder/decoder 210 couples to the data bus DQ intervening between the logic IC 14 and the modified RAM ICs 216.sub.x. Additionally, at least one DBI bit is included with data bus DQ. To handle this DBI bit, each of the modified RAM ICs 216.sub.x includes a DBI storage area 225.

(23) Further details concerning such an implementation of DBI in system 200 is shown in FIG. 6. As can be seen, it is assumed that the modified RAM IC 216.sub.x in this example comprises a X8 device, in which eight bits (i.e., a byte) is written/read to/from the modified RAM ICs 216.sub.x at one time. The array of memory cells 61 in the modified RAM IC 216.sub.x includes areas in which each of the eight bits DQ1-8 are stored. Additionally, and as just mentioned, a dedicated. DBI storage area 225 is also present for the DBI bit. In effect, the modified RAM IC 216.sub.x comprises in this example a X9 device comprising at each address a data byte and its associated DBI bit. As one skilled in the art will realize, the areas dedicated to the data and the DBI bit 225 can occur in different locations on the modified RAM IC 216.sub.x, and need not appear as depicted as contiguous rectangles.

(24) DBI encoding and decoding in the depicted example are implemented by encoding 210a and decoding 2101 circuitry. Such circuitry 210a and 210b, in this embodiment, is present only on the logic IC 14 as opposed to the modified RAM ICs 216.sub.x, which is consistent with the desired intention in system 200 to move as much of the logic circuitry off of the modified RAM ICs 216.sub.x and onto the logic IC 14 as possible.

(25) When writing to the modified RAM IC 216x (or more generally, the memory set 25), data is presented from the memory controller 12 to the logic IC 14 on bus DQ, along with the appropriate address for that data and a write command as embodied in the signals present on control bus, cntl. (The address bus from the memory controller 12, A, is not shown in FIG. 6 for clarity, but may share a bus with the control signals in a time multiplexed fashion). A command decoder 240 on the logic IC 14 interprets the write command and enables the encoder 210a via a write enable signal, W/E. The encoder 210a may be similar to that shown earlier in FIGS. 2A and 2B, and will operate in accordance with a desired DBI algorithm, of which many exist. The encoder 210a assesses the incoming bytes of data on DQ, and issues new data DQ and a DBI bit in accordance with the DBI algorithm. Data DQ may there be completely or partially inverted depending on the algorithm and the state of the given DBI bit. In any event, a given encoded data byte DQ is stored with its DBI bit at the appropriate address in the modified RAM IC 216.sub.x.

(26) Reading from the modified RAM IC 216.sub.x (i.e., from memory set 25) requires decoding of the stored data in accordance with the DBI bit stored with that data. This occurs as follows. Control decoder 240 on the logic IC interprets a read command, and enables the decoder 210b via read enable signal, R/E. Encoded data is then read at the specified address from the modified. RAM IC 216.sub.x on bus DQ along with the DBI stored at that address. The decoder 210b interprets the DBI bit, and decodes, i.e., completely or partially un-inverts the data as necessary, and passes the decoded data to the memory controller 12 via bus DQ.

(27) This example allows for the implementation of DBI without requiring the modified RAM ICs 216.sub.x to have any DBI logic circuitry whatsoever. However, in this embodiment, the modified RAM ICs 216.sub.x will need to store the DBI bit, which will either require the modified RAM ICs 216.sub.x to increase in size, or to store less data within the nominal size.

(28) Another embodiment of the disclosed DBI technique that does not require storage of the DBI bits is shown in the system 200 of FIG. 7A, in this embodiment, the modified RAM ICs do not require an additional DBI storage area 225, and hence can be the same as the modified RAM ICs 16.sub.x discussed in conjunction with FIGS. 3A and 3B. However, in this embodiment, one of the modified RAM ICs, specifically RAM IC 250, is dedicated to the storage of DBI bits. Such an architecture for system 200 is logically implemented assuming the modified RAM ICs 16.sub.x and 250 are x1 devices. Accordingly, when a byte of data is written to the modified RAM ICs 16.sub.x (i.e., memory set 25), each bit in the encoded byte is sent to a particular one of the modified RAM ICs 16x, i.e., RAM IC 16.sub.1 receives DQ1, etc., and the DBI bit gets stored in parallel in modified RAM IC 250. Thus, a given address in this example causes writing to/reading from all of the modified RAM ICs in the memory set 25. While this implementation requires no further modifications to the modified RAM ICs 16.sub.x and 250, it will require an additional modified RAM IC 250 to be present in the module 40 if the same amount of data is to be stored, as shown in FIG. 7B.

(29) If it is undesired or impossible to include an additional modified RAM IC 250 within the module 40 as shown in FIGS. 7A and 7B, one could substitute the modified RAM IC 250 within the module 40 for RAM residing outside of the module 40. For example, other RAM 260 shown in dotted lines in FIG. 7A, could be used for storage of the DBI bit, which other RAM 260 could appear outside of the module 40, such as for example, in the logic IC 14, in the memory controller 12, or as a separate device in the system 200. So long as such other RAM 260 is connected to the same address as its encoded data in the modified RAM ICs 16.sub.x, proper DBI encoding and decoding can be established.

(30) FIGS. 8A-8C illustrate another embodiment of a system 300 implementing the disclosed DBI technique in which DBI is applied to the data in only one direction of the data flow between the logic IC 14 and the memory 25. Specifically, in the depicted embodiment, DBI is applied to reduce data transmissions only when writing data to the memory set 25. Accordingly, logic IC 14 only contains a DBI encoder 210a, as shown in FIGS. 8A and 8B. The corresponding decoder for this one-way DBI implementation appears on the modified RAM ICs 316.sub.x as decoder block 310.

(31) Operation of the one-way DBI algorithm in system 300 is explained further in FIGS. 8B and 8C. As shown, encoded data. DQ(1:8), encoded via a suitable DBI algorithm at encoder 210a on the logic IC 14, is sent to modified RAM ICs 316.sub.x via bus 15. Each of the modified RAM ICs 316.sub.x contains a decoder 310. When writing is taking place, command decoder 240 (which can be present on the logic IC 14, the modified RAM ICs 316.sub.x, or elsewhere), issues a write enable signal. W/E, which enables both the encoder 210a on the logic IC 14. This causes encoder 210a to issue encoded data DQ on bus 15, which may or may not be completely or partially inverted depending on the DBI algorithm being used.

(32) In any event, while writing (i.e., while W/E is asserted), decoder 310 will take the encoded data DQ after transmission on the bus 15 and un-invert such data as mandated by the DBI bit at the modified RAM ICs 316.sub.x. Such decoding can be accomplished by the simple utilization of XOR gates 315 for each of the data channels, DQ, as shown in FIG. 8C. In this embodiment, decoder 310 can always remain enabled, as XOR gates only consume power during transitions. However, the W/E signal may still be used to enable other aspects of the receiving circuitry within memory set 25. Assuming the implementation of a simple minimum transitions DBI algorithm, decoder 310 will include eight XOR gates, i.e., one for each of the data bits from the byte, which XOR gates receive at their inputs the current DBI bit and one of the bits in the encoded byte. If inversion occurred for a given byte of data (i.e., if DBI=1), XOR gates 315 will un-invert the data, producing true, un-encoded data bytes DQ.sub.array(1:8) which will be stored in the modified RAM ICs 316.sub.x.

(33) To reiterate, by operation of the DBI encoder 210a on the logic IC 14 and decoder 310 on the RAM ICs 316.sub.x, data is or is not inverted during transmission to the modified RAM ICs 316.sub.x across bus 15 to improve power consumption, data integrity, and reliability. But, the inverted data is then decoded and stored in its true state in the array of cells 61 of those RAM ICs 316.sub.x. By contrast, when reading from system 300, no DBI algorithm operates in this embodiment, and instead the true data is merely read from the modified RAM ICs 316.sub.x and is transmitted back across bus 15 without encoding.

(34) As a result, and beneficially, in this embodiment of FIGS. 8A-8C, there is no need to store the DBI bit, because the data is decoded by decoder 310 on the modified RAM ICs 316.sub.x before it is written into the RAM ICs. Provisions therefore do not need to be made, as in earlier embodiments, to provide a DBI storage area 225 on the modified RAM ICs 316.sub.x (FIGS. 5 and 6), nor is a dedicated DBI storage modified. RAM ICs 250 necessary (FIGS. 7A and 7B).

(35) However, this embodiment does require that the modified RAM ICs 316.sub.x include a DBI decoder 310. Generally, the provision of such a decoder 310 on the modified RAM ICs 316.sub.x is contrary to the desire that the modified RAM ICs contain as little excess circuitry as possible. But as shown in FIG. 8C, such a DBI decoder 310 can require little more than the inclusion of XOR gates 315 or other simple digital logic gates on the modified RAM ICs 316.sub.x, which additional decoding logic 310 is negligible in the context of the modified RAM IC 316.sub.x, and takes up minimal layout area on the modified RAM ICs 316.sub.x. For clarity's sake, it is repeated here that although the implementations described herein function with only one DBI bit, more complex DBI algorithms could be implemented which might require multiple DBI bits.

(36) In another embodiment (not shown), the DBI encoder can be provided on the modified RAM ICs, while a DBI decoder is present on the logic IC 14. This presents essentially the reverse of the one-way DBI technique discussed in FIGS. 8A-8C, such that DBI operates when reading from the memory set 25, but does not operate when writing to the memory set 25. While such an implementation would certainly be functional, provision for DBI encoder circuitry on the modified RAM ICs may be incompatible with the goals of the system. This is because encoding circuitry may take a significant amount of area (at least, compared to the decoder) to accommodate the analog circuitry (e.g., operational amplifiers, etc.) such encoders typically require. As such, encoding circuitry may be better relegated to the logic IC 14 in a system in which the modified RAM ICs 316.sub.x are made as small as possible.

(37) Any of the DBI implementation set forth in FIGS. 5-8C can be implemented in a system in which the data is fully or partially decoded, as shown in FIG. 3B. However, such systems that in effect combine the system of FIG. 39 with the systems of FIGS. 5-8C are not illustrated because such an extension of the disclosed techniques should be apparent to one skilled in the art on the basis of this disclosure.

(38) While envisioned for use with discrete integrated memory circuits, the disclosed technique can be used more generally with any memory structure having storage cells, even if not a discrete integrated circuit. For example, a plurality of memory sub-arrays could operate as the plurality of memory structures useable in the technique, even if such sub-arrays are themselves integrated on a single integrated circuit. Additionally, while illustrated in the context of a plurality of memory ICs (or a plurality of memory structures more generally), it should be noted that the disclosed technique still has applicability when used with a single memory IC (or memory structure).

(39) As noted earlier, many different types of DBI algorithms exist. Different DBI algorithms are beneficial in different circumstances, and not all DBI algorithms are directed to minimizing the number of data transition across transmission channels. For example, other well-known DBI algorithms include the minimum zeros algorithm and the minimum ones algorithm. The purpose of these algorithms is, respectively, to minimize the number of binary zeros or binary ones transmitted across a channel. Such minimum zeros or ones algorithms conserve power when the driver or receiver circuits coupled to the transmission channels are not full CMOS and therefore will draw more power when transmitting or receiving a particular data state. For example, if a pull-up resistor connected to the voltage supply is used in a particular driver circuit, driving a logic 0 will require more power than would driving a logic 1. As a result, use of a minimum zeros DBI algorithm would be warranted. Likewise, if a pull-down resistor is used, a minimum ones algorithm would be warranted. The minimum transitions and either of the minimum zeros or ones algorithms can also be combined in a DBI algorithm, as is disclosed in U.S. patent application Ser. No. 12/015,311, filed Jan. 16, 2008. In another DBI algorithm, discussed in the above-mentioned Ser. No. 11/873,779 application, only a portion of the data bits on a bus are inverted to balance the logic states in an encoded byte across the bus, which can be referred to as a Balanced DBI algorithm. Regardless of the DBI algorithm used, all of these DBI algorithms have the common feature of sequentially receiving groups of N original data bits and selectively encoding each group to form a corresponding group of N encoded data bits while issuing at least one encoding (DBI) indicator associated with each group of the N encoded data bits. Any of these DBI algorithms can be used in the context of the disclosed embodiments of the invention, and therefore the illustration or focus given to the minimum transition DBI algorithm should be understood as merely exemplary and non-limiting.

(40) While some implementations have been disclosed, it should be understood that the disclosed circuitry can be achieved in many different ways to the same useful ends as described herein. In short, it should be understood that the inventive concepts disclosed herein are capable of many modifications. To the extent such modifications fall within the scope of the appended claims and their equivalents, they are intended to be covered by this patent.