Testing and repair of embedded memory

Abstract: A method and circuits for coupling a memory embedded in an integrated circuit to interconnect pads during a memory test mode is disclosed. The integrated circuit contains a processor, an embedded memory and a switching circuit for: (1) temporary coupling the interconnect pads of the integrated circuit, coupled to the processor during normal operation mode of the circuit, to the memory during a memory test mode; (2) and decoupling the external interconnect pads from the memory, after the memory is tested, and coupling them to the processor.

Description: This application is related to European Patent Application No 97302105.8 filed simultaneously herewith and based on US Patent Application No 08/626540 filed 2 April 1996 (Attorney Reference: PWF 82811). The present invention relates to the field of electronic devices having embedded memory, and is more specifically directed to the testing and optionally repairing of the embedded memory. Embedded memory is memory that is embedded with a processor. The embedded memory can be the memory necessary for the core functionality of the processor, it can also be the data storage memory, where the data that the processor processes is stored. Many processors contain a small amount of memory, typically on the order of several kilo bit, which is typically arranged into memory registers and is necessary for the core functionality of the processor. The data storage memory is much larger than the memory that is needed for the processor for its core functionality. Currently this memory is usually external memory, i.e. it is not embedded on the same integrated circuit that the processor is on because of the low yield of the process in manufacturing the circuit and the expense of testing and repairing the memory. A goal in the semiconductor industry is to increase the speed of the processor. One way to increase the speed of the processor is to embed the memory used for data storage into the processor. When memory used for data storage is on a separate chip than the processor the two chips must be electrically coupled. The input/output pins of the processor are coupled to the input/output pins of the memory by external metal connections. This increases the amount of time it takes for the processor to read data out of the memory and write data into the memory. Embedding the memory into the processor reduces the amount of time the processor takes to access the memory. Additionally, since the memory now does not require the external input/output pins previously needed for coupling to the processor, the packaging cost of the memory is greatly reduced. Furthermore, the memory can now be specifically configured for the processor into which it is embedded. Embedding the memory in the processor also eliminates the need for the external metal connections, increasing the accuracy of the connections in the combined product. For example, a standard memory device design can be embedded in the processor, with the memory array and peripheral circuits needed to operate the memory array coupled to the processor. Since most standard memory devices have input/output pads, the embedded memory would have the input/output pads but they would be disconnected from the memory array and memory peripheral circuits. Although, since the input/output pads are disconnected from the memory array and peripheral circuits, they are not necessary for the functioning of the memory and may be removed. This frees up the space previously occupied by these pads, thereby reducing the total size of the memory. However, this would require a memory devices manufactured without the input/output pads. Both the memory and the processors are tested to ensure that they do not malfunction. Every cell in a memory is typically tested to ensure that there are no defective cells. A fatal defect in one memory cell makes the cell inoperable. If the cell is not replaced the entire memory device can malfunction. Therefore, a defective memory cell must either be replaced, or the entire chip discarded. When the memory is embedded in a processor the cost of discarding the chip increases. As the component size is reduced and the density of components per unit area of a semiconductor device is increased, the costs of the device decreases while its speed increases. However, as the size of components decreases and their density increases the size of a defect that can cause failure also shrinks. Additionally, as the speed with which processors process data increases, the amount of data that can be made available to the processors also increases, usually by increasing the size of the memory for storing data. As the size of and total number of components in a memory device continues to increase, so does the cost of each memory device, and therefore the cost of each non-usable memory device. Redundant columns and/or rows are often used in memory devices to prevent an isolated defect from destroying the entire device. The decision on whether to use redundant columns and/or rows is based on balancing the additional die space needed for the redundancy architecture and the yield of the manufacturing process if redundancy is not used. If the yield is high enough, it is cheaper to discard the few memories with defective cell than add the redundancy architecture to each memory. If the yield is not sufficiently high, the redundancy architecture can greatly decrease the yield loss in these memory devices by replacing a column or row containing a defect in one of its memory cells with a redundant column or row. This can save a memory device that would otherwise have been unusable. The defects in the memory cells are discovered in initial testing, and the redundant columns or rows can then be activated to replace the columns or rows containing defective cells. Extensive testing is performed on the memory to determine which if any of the memory cells are defective. The test equipment for testing memories is coupled to the input/output pads of the memory. When a memory is embedded into the processor this is usually is not possible. There are either no external input/output pads on the memory for the test equipment to connect to; or some external input/output pads remain, but not enough to test every memory cell. Thus the memory must be tested through the processor. Processors are also tested to ensure that they function properly. The test equipment for testing processors is coupled to the input/output pads of the processor. A problem in the prior art is that the cost of testing a chip increases when a memory is embedded in a processor. This is especially true for the testing required to discover which memory cell is defective. To find exactly which memory cell is defective the memory must be extensively tested. In modern technology, embedded memory is tested through the processor, using the input/output pads of the processor since the memory does not have, or does not have enough of, its own input/output pads. The testing equipment for the processors is at least several times more expensive than comparable testing equipment for memories. Both the memory and the processor must now be tested on the processor testing equipment, increasing the amount of time each chip is required to spend on the processor testing equipment by the amount of time it takes to perform the memory tests. Therefore, either: (1) more very expensive processor testing equipment must be used to test both the processor and the memories which can now only be tested through the processor, drastically increasing the cost of each chip; or (2) the cycle time of producing a given number of processors containing embedded memories will be much larger than for processors without embedded memories. Both of these increase the cost of the chip, whether the memory will be repaired or not, since either way each memory cell must still be tested. Although when the memory will also be repaired the test time and therefore the cost is even greater. When the memory is small this increase is small. However, when the memory is the size of a memory used for data storage, which can range from hundreds of kilo bits to many Mega bits or more, this increase is prohibitively expensive. This makes the cost of embedding memories for data storage into processor impractical despite all the advantages, described above, obtained from embedding the memory into the processor, and hinders the achievement of the long recognized goal to increase the speed with which the processor can access data. US-A-3961251 whereon the preamble of claims 1 and 15 is based describes a semi-conductor device which has a plurality of logic circuits and a memory array. The logic circuits may be for example registers, decoders etc. Primary inputs are provided. These inputs are input to the logic circuits. Additionally, some of these inputs are additionally arranged to bypass the logic and be input to address gates, forming part of the memory array. The address gates are arranged in a test mode to receive data which has bypassed the logic circuit and in a normal mode to receive data from the logic circuit. The logic circuit can be tested. This involves writing data to the memory. The memory then becomes a stored table by which the logic can be tested. According to a first aspect of the present invention there is provided a method for testing an integrated circuit containing both memory and logic comprising the steps of: temporarily coupling said memory to one or more interconnect pads through a respective one or more switching circuit, each having a respective control input, responsive to a second logic state received at the control input; testing said memory; decoupling said memory from said one or more interconnect pads; and coupling said logic to said one or more interconnect pads through said respective one or more switching circuits responsive to a first logic state received at the control input. The method may further comprise the step of repairing said memory, conditionally performed after said step of testing said memory. Said step of repairing said memory may comprise replacing defective memory cells with redundant memory cells. Each one of one or more switching circuits, having a control input, may be coupled to said memory, and coupled to said logic responsive to a first logic state received at said control input, and coupled to one of each said memory interconnect pads responsive to a second logic state received at said control input. Said step of decoupling said memory from said interconnect pads may be responsive to a first logic state received at said control input. The method may further comprise coupling said interconnect pads to memory test equipment, performed before said step of testing said memory, setting a flat bit to a third logic state for signifying said memory is non-defective and to a fourth logic state for signifying said memory is defective, performed after the step of testing said memory, decoupling said memory from said memory test equipment, responsive to said third logic state at said flag bit, coupling said processor to said interconnect pads, coupling said interconnect pads to processor test equipment, testing said processor, and decoupling said interconnect pads from said processor test equipment. Responsive to said third logic state at said flag bit the method may further comprise the step of final testing said integrated circuit, performed after said step of testing said processor. Embodiments of the present invention may provide a method of testing an integrated circuit containing a processor and an embedded memory comprising the steps of coupling said memory to one or more interconnect pads, testing said memory, decoupling said memory from said interconnect pads, and coupling said processor to said interconnect pads. The method may further comprise the step of testing said processor, performed after said step of coupling said processor to said interconnect pads. The method may further comprise the steps of coupling said processor to said interconnect pads, testing said processor, and decoupling said processor from said interconnect pads, wherein said step of coupling said memory to one or more interconnect pads is performed after said step of decoupling said processor from said interconnect pads. Said step of decoupling said processor from said interconnect pads and said step of coupling said memory to said interconnect pads may be performed simultaneously. The method may further comprise the step of repairing said memory, conditionally performed after said step of testing said memory. Said step of repairing said memory may comprise replacing defective memory cells with redundant memory cells. The method may further comprise one or more switching circuits having a control input, each one of said switching circuits coupled to said memory, and coupled to said processor responsive to a first logic state received at said control input, and coupled to one of each said memory interconnect pads responsive to a second logic state received at said control input. Said step of decoupling said memory from said interconnect pads may be responsive to a first logic state received at said control input. Said step of decoupling said memory from said interconnect pads and said step of coupling said processor to said interconnect pads may be performed simultaneously. The method may further comprise the step of final testing said integrated circuit, performed after said step of coupling said processor to said interconnect pads. According to a second aspect of the present invention there is provided an integrated circuit comprising: a logic; a memory; one or more interconnect pads; one or more switching circuits, each having a control input, each coupled at one end to one of said interconnect pads, and each coupled at another end to said processor in response to a first logic state received at said control input, and each coupled at said another end to said memory in response to a second logic state received at said control input. The integrated circuit may further comprise a memory test circuit coupled to each said control input for controlling said switching circuit. The integrated circuit may further comprise a current limiting device coupled between ground, and said memory test circuit and said switching circuit. Said current limiting device may comprise a transistor having a length and a width, wherein said length is greater than said width. Each said switching circuit may couple said processor to said interconnect pads and may decouple said memory from said interconnect pads responsive to a first logic state at said control input. Each said switching circuit may couple said memory to said interconnect pads and may decouple said processor from said interconnect pads responsive to a second logic state at said control input. Each said switching circuit may comprise a first and a second pair of pass elements. Each said pass element may consist of an n-channel transistor. Said processor may be any one of a digital signal processor, a microprocessor, a video compression device, or a DRAM. Embodiments of the present invention may provide a computer comprising an input device, an output device, and an integrated circuit coupled to said input device and said output device comprising a processor a memory array, one or more switching circuits having a control input, each coupled to one of said interconnect pads, and coupled to said processor responsive to a first logic state received at said control input, and coupled said memory responsive to a second logic state received at said control input. The computer may further comprise a memory test circuit coupled to each said control input for controlling said switching circuit. The computer may further comprise a current limiting device coupled between ground, and said memory test circuit and said switching circuit. Said current limiting device may comprise a transistor having a length and a width, wherein said length is greater than said width. Each said switching circuit may couple said processor to said interconnect pads and decouple said memory from said interconnect pads responsive to a first logic state at said control input. Each said switching circuit may couple said memory to said interconnect pads and may decouple said processor from said interconnect pads responsive to a second logic state at said control input. Each said switching circuit may comprise a first and a second pair of pass elements. Each said pass element may comprise a pass gate having a pair of complementary transistors with their conduction paths coupled in parallel. Said processor may be a microprocessor. Said memory may be a DRAM. The present application discloses a method and circuits for coupling an embedded memory to the interconnect pads through a switching circuit during a memory test mode. This allows the memory to be coupled through the interconnect pads to memory test equipment, and to be tested on memory test equipment; instead of being tested on the processor test equipment. In the memory test mode the memory is coupled to the interconnect pads. In the normal operation of the circuit the processor, to which the memory is coupled to, is coupled to the interconnect pads. A significant advantage of embodiments of the present invention is that the majority of the memory testing can be performed using the less expensive memory test equipment instead of the more expensive processor test equipment. Another advantage of embodiments of the present invention is that a memory without its own memory interconnect pads can be used, or the number of memory interconnect pads can be reduced, saving die space. Other advantages and objects of embodiments of the invention will be apparent to those of ordinary skill in the art having reference to the following specification together with the drawings. Figure 1 is an electrical diagram, in block form, of an integrated circuit containing embedded memory according to an embodiment of the present invention. Figure 2 is an electrical diagram, in schematic form, of the integrated circuit of Figure 1 containing one embodiment of the switching circuit according to the present invention. Figure 3 is an electrical diagram, in schematic form, of the integrated circuit of Figure I containing another embodiment of the switching circuit according to the present invention. Figure 4 is an electrical diagram, in block form, of a computer containing the integrated circuit containing embedded memory embodying the present invention. Figure 1 shows an integrated circuit 10 containing an embedded memory according to an embodiment of the present invention. Integrated circuit 10 contains a memory 12, a processor 14, and interconnect pads 20 0 , ... 20 N . The memory 12 is coupled to the processor 14. In the current technology DRAMS are typically used for data storage, although any conventional memory can be used, such as SRAMs, which can be more compatible with the processor fabrication technology. Each of the interconnect pads 20 0 , ... 20 N can be an input/output pad, just an input pad, or just an output pad depending on the functionality of the integrated circuit's 10 component that the pad is coupled to. Input circuits 22 0 , ... 22 N are coupled to the input/output pads and to input pads, and output circuits 24 0 , ... 24 N are coupled to the input/output pads and to output pads. Electrostatic-discharge protection components can be coupled to the interconnect pads 20 0 , ... 20 N . Switching circuits 26 0 , ... 26 N are coupled to the interconnect pads 20 0 , ... 20 N . Switching circuits 26 0 , ... 26 N are also coupled to the memory 12 and processor 14. The switching circuits 26 0 , ... 26 N are controlled by a memory test circuit 28. The output of the memory test circuit is coupled to the control input of each of the switching circuits. The memory test circuit can be located anywhere on the integrated circuit 10. In the preferred embodiment, the memory test circuit 28 is simply a memory test pad (hereinafter memory test pad 28), although any conventional memory test circuit that is capable of producing two distinguishable logic states at its output can be used. A current limiting device 29 is coupled between the output of the memory test pad 28 and the control inputs of the switching circuits 26 0 , ... 26 N . The current limiting device 29 can be any device that reduces or eliminates the power dissipation when the memory test pad is low. The current limiting device 29 can be any device that produces a large resistance, and is preferably an n-channel transistor (hereinafter transistor 29) whose length is much greater than its width. The length to width ratio of transistor 29 in the preferred embodiment is on the order of 100 to 1. The switching circuits 26 0 , ... 26 N allow the interconnect pads 20 0 , ... 20 N to be coupled to the memory 12 or to the processor 14. There must be enough switching circuits 26 0 , ... 26 N such that enough interconnect pads 20 0 , ... 20 N can be coupled to the memory 12 to allow the memory 12 to be coupled to memory test equipment and tested. In the integrated circuit 10 shown in Figure 1 all of the interconnect pads 20 0 , ... 20 N are coupled to a switching circuit 26 0 , ... 26 N , respectively. However, in alternative embodiments of the invention some interconnect pads 20 0 , ... 20 N may be coupled to just the processor 14, or just to the memory 12. One of the interconnect pads 20 0 , ... 20 N is coupled to the input of each of the switching circuits 26 0 , ... 26 N , respectively. The processor 14 is coupled to the first output of each of the switching circuits 26 0 , ... 26 N . The memory 12 is coupled to the second output of each of the switching circuits 26 0 , ... 26 N . In the normal operation of the circuit the processor 14 is coupled to the interconnect pads 20 0 , ... 20 N through the switching circuits 26 0 , ... 26 N responsive to a first logic state on the memory test pad 28. The first logic state is preferably low since this does not require the memory test pad 28 to dissipate power during the normal operating mode of the integrated circuit 10, which it is in most of the time. In the preferred embodiment of the invention, the memory is not coupled to the interconnect pads 20 0 ... 20 N in the normal operation of the circuit. When the circuit enters the normal operation mode interconnect pads 20 0 ... 20 N are coupled to the processor 14. When the circuit 10 enters the normal operation mode from the memory test mode the interconnect pads 20 0 ... 20 N are decoupled from the memory 14 and coupled to the processor 14. In the preferred embodiment of the invention this occurs simultaneously. In a memory test mode, the logic state on the memory test pad 28 is high causing the switching circuit to couple the interconnect pads 20 0 ... 20 N to the memory 12, and to decouple the interconnect pads 20 0 ... 20 N from the processor 14 if they are coupled to the processor 14 when the circuit enters the memory test mode. In the preferred embodiment of the invention this occurs simultaneously when the circuit enters the memory test mode. Coupling the memory 12 to the interconnect pads 20 0 ... 20 N allows the interconnect pads to control the memory 12. The interconnect pads 20 0 ... 20 N can be coupled to the memory test equipment and the memory 12 can be tested. This initial testing is typically quite thorough and the defects in the memory cells are usually discovered during this initial testing. If redundant columns or rows are available in the memory, the redundant columns or rows can now be activated to replace the columns or rows containing defective cells. Extensive testing is performed on the memory to determine which if any of the memory cells are defective. The decision on whether to use a redundancy architecture is based on balancing the additional die space needed for the redundancy architecture and the yield of the manufacturing process if redundancy is not used. If the yield is high enough, it is cheaper to discard the few memories with defective cell than add the redundancy architecture to each memory. If the yield is not sufficiently high, the redundancy architecture can greatly decrease the yield loss in these memory devices by replacing a column or row containing a defect in one of its memory cells with a redundant column or row. This can save a device that would otherwise have been unusable. The processor is tested to ensure that it functions properly. The processor can be tested before or after the memory is tested. Connections between the memory and the processor are also tested. The connections are tested by accessing the memory thorough the processor. Testing the connections is a much shorter test then the initial memory test, not requiring long use of the expensive processor test equipment. The processor and the connections are typically tested in the electronic wafer sort. In the prior art the processor and embedded memory are tested in a continuous process. In the preferred embodiment of the invention, the memory is tested first on separate memory testing equipment, and a flag bit in the memory is set to a third logic state to mark that memory is non-defective or to a forth logic state to mark that the memory is defective. If the flag bit is set to the third logic state the die is tested in the electronic wafer sort. After both the processor and the memory are tested, and typically after the integrated circuit 10 is packaged, the final test is performed on the integrated circuit 10. The memory is usually tested through the processor in the final test. The memory is tested for again a much shorter time in the final test then in the initial memory test. Coupling the memory 12 to the interconnect pads 20 0 ... 20 N permits majority of the memory testing to be performed on the much less expensive memory test equipment instead of on the much more expensive processor test equipment. Figure 2 shows one placement of one embodiment of the switching circuit 26 0 coupled to the memory 12, the processor 14, one placement of the interconnect pad 20 0 , one placement of the input circuit 22 0 , and one placement of the output circuit 24 0 . In the preferred embodiment of the invention input circuit 22 0 is an inverter 40 0 , and output circuit 24 0 is several inverters connected in series, 42 0 , 44 0 , 46 0 , although any conventional input circuit and any conventional output circuit can be used. Switching circuit 26 0 contains a first and second pair of pass elements. In one preferred embodiment of the switching circuit 26 0 pass elements are pass gates 50 0 , 56 0 , 52 0 , 54 0 , of complementary transistors with their conduction paths connected in parallel, although any other conventional component or combination of components for passing a signal, such as a single transistor can be used. Figure 3 shows another preferred embodiment using a single n-channel transistor as a pass element. Referring again to Figure 2, the first pair of pass gates 50 0 , 56 0 are coupled between the interconnect pad 20 0 and the processor 14. The second pair of pass gates 52 0 , 54 0 are coupled between the interconnect pad 20 0 and the memory 12. The pass gates are controlled by the memory test pad 28 and an inverter 48 0 coupled to the p-channel transistors of the second pair of pass gates 52 0 , 54 0 and to the n-channel transistors of the first pair of pass gates 50 0 , 56 0 . When the logic state on the memory test pad 28 is low, the first pair of pass gates 50 0 , 56 0 are on coupling the interconnect pad 20 0 to the processor 14. The second pair of pass gates 52 0 , 54 0 are off, decoupling the interconnect pad 20 0 from the memory 12. When the logic state on the memory test pad 28 is high, the second pair of pass gates 52 0 , 54 0 are on, coupling the interconnect pad 20 0 to the memory 12. The first pair of pass gates 50 0 , 56 0 are off, decoupling the interconnect pad 20 0 from the processor 14. Figure 3 shows one placement of another preferred embodiment of the switching circuit 26 0 coupled to the memory 12, the processor 14, and one placement of the interconnect pad 20 0 . The first and second pair of pass elements in this embodiment of the switching circuit 26 0 are n-channel transistors 60 0 and 66 0 , and 62 0 and 64 0 , respectively. The first pair of transistors 60 0 , 66 0 are coupled between the interconnect pad 20 0 and the processor 14. The second pair of transistors 62 0 , 64 0 are coupled between the interconnect pad 20 0 and the memory 12. The first pair of transistors 60 0 , 66 0 are controlled by the memory test pad 28 and an inverter 48 0 coupling the interconnect pad 20 0 to the processor 14 when the logic state on the memory test pad 28 is low and decoupling the interconnect pad 20 0 from the processor 14 when the logic state on the memory test pad 28 is high. The second pair of transistors 62 0 and 64 0 are controlled by the memory test pad 28, coupling the interconnect pad 20 0 to the memory 12 when the logic state on the memory test pad 28 is high and decoupling interconnect pad 20 0 from the memory 12 when the logic state on the memory test pad 28 is low. Therefore embodiments of the invention allow a memory to be embedded in a processor, and tested using the interconnect pads 20 0 ... 20 N . This provides the advantages of reducing the access time of the memory and the cost of the memory by embedding a memory without the increased costs of fully testing the embedded memory on the more expensive processor test equipment. Additionally, since the memory is tested on the integrated circuits interconnect pads 20 0 ... 20 N , the memory interconnect pads are not needed and the memory can be manufactured without them, providing space savings on each embedded memory. Embedding a memory in a processor, and testing the memory using the interconnect pads 20 0 ... 20 N is accomplished through the above described method of temporarily coupling the memory to one or more of the interconnect pads, testing the memory, and decoupling said memory from the first interconnect pads. The processors with embedded memories can be used in computers, as shown in Figure 4. This type of integrated circuit 10 is also particularly useful in medical equipment where quick access to the data stored in the memory can increase the accuracy as well as the speed of the equipment. Embodiments of the invention are also useful in designing custom processors with chip cache memory. It is particularly useful in graphics devices where quicker access by the processor to the data stored in memory can improve the resolution and detail of both two and three dimensional graphics. Further background on memories and on the testing and repairing of memories and processors can be found in: Prince, Betty, SEMICONDUCTOR MEMORIES, A HANDBOOK OF DESIGN, MANUFACTURE, AND APPLICATION, 2 nd ed., John Wiley & Sons, 1991; Zaks, Rodnay, and Alexander Wolfe, FROM CHIPS TO SYSTEMS: AN INTRODUCTION TO MICROCOMPUTERS, 2 nd ed., SYBEX, 1987; and the ISSCC proceedings from 1975 to the present, all incorporated herein by reference. While the invention has been specifically described with reference to several preferred embodiments, it will be understood by those of ordinary skill in the prior art having reference to the current specification and drawings that various modifications may be made and various alternatives are possible therein without departing from the invention as defined in the claims. For example: Although the embodiments of the invention are described in relation to a DRAMs or SRAMs the invention can be used in other types of memories including read-only memories, FIFOs, EPROMs, EEPROMs, or flash memories without departing from the scope of the invention. A microprocessor, microcontroller, digital signal processor, or any application specific integrated circuit that can process data can be used as the processor without departing from the scope of the invention. Although the embodiments of the invention are described using a processor any logic that can process data can be used. While the embodiments of the invention have been described as particularly useful in certain application, it can be used anywhere a processor and memory are used, and is particularly useful where quick access to the data stored in the memory is desired. Although the external interconnect pads are all shown in Figure 1 as input/output pads, some or all of the external interconnect pads can be just input pads or just output pads. While the memory interconnect pads are all shown in Figure 1 as input/output pads, some or all of the memory interconnect pads can be just input or just output pads.

Claims: A method for testing an integrated circuit (10) containing both memory (12) and logic (14) comprising the steps of: temporarily coupling said memory to one or more interconnect pads (20) through a respective one or more switching circuit (26), each having a respective control input, responsive to a second logic state received at the control input; testing said memory (12); decoupling said memory (12) from said one or more interconnect pads; and characterised in coupling said logic to said one or more interconnect pads (20) through said respective one or more switching circuits (26) responsive to a first logic state received at the control input. The method of claim 1, further comprising: coupling said interconnect pads (20) to memory test equipment, performed before said step of testing said memory; setting a flag bit to a third logic state for signifying said memory is non-defective and a fourth logic state for signifying said memory is defective, performed after the step of testing said memory; decoupling said memory from said memory test equipment; responsive to said third logic state at said flag bit: coupling said logic to said interconnect pads; coupling said interconnect pads to logic test equipment; testing said logic ; and decoupling said interconnect pads from said logic test equipment. The method of claim 2, responsive to said third logic state at said flag bit, comprising the step of final testing of said integrated circuit, performed after said step of testing said logic. The method as claimed in any preceding claim, wherein said logic comprises a processor. A method as claimed in any preceding claim, wherein said memory is an embedded memory. The method of any preceding claim further comprising the step of: decoupling said logic from said interconnect pads; wherein said step of coupling said memory to one or more interconnect pads is performed after said step of decoupling said logic from said interconnect pads. The method of claim 6 wherein the step of decoupling the logic is in response to the second logic state on the control input. The method of claims 6 or 7 wherein the step of decoupling one of the logic and the memory and the step of coupling the other of the memory and the logic are performed simultaneously. The method of any preceding claim, wherein the memory is tested before or after the logic. The method as claimed in any preceding claim, comprising the step of final testing of said integrated circuit. The method of any preceding claim further comprising the step of repairing said memory, conditionally performed after said step of testing said memory. The method of claim 11, wherein said step of repairing said memory comprises replacing defective memory cells with redundant memory cells. The method of any preceding claim, wherein said memory is decoupled from said one or more interconnect pads in response to the first logic state received as said control inputs. The method of any preceding claim, comprising the step of testing said logic performed after the step of coupling said logic to said one or more interconnect pads. An integrated circuit comprising: logic (14) a memory (12) one or more interconnect pads (20); one or more switching circuits (26), each having a control input, each coupled at one end to one of said interconnect pads, and each coupled at another end to said memory in response to a second logic state received at said control input, characterised in that each switching circuit (26) is coupled at said another end to said logic (14) in response to a first logic state received at said control input. The integrated circuit of claim 15 further comprising a memory test circuit (28) coupled to each said control input for controlling said switching circuit (26). The integrated circuit of claim 15, further comprising a current limiting device (29) coupled between ground, and said memory test circuit and said switching circuit. The integrated circuit of claim 17, wherein said current limiting device comprises a transistor having a length and a width, wherein said length is greater than said width. The integrated circuit of any of claims 15 to 18, wherein each said switching circuit decouples said memory from said interconnect pads responsive to a first logic state at said control input. The integrated circuit of any of claims 15 to 19, wherein each said switching circuit decouples said processor from said interconnect pads responsive to a second logic state at said control input. The integrated circuit of any of claims 15 to 20 wherein each said switching circuit comprises a first and second pair (50,56,52,54;60,66,62,64) of pass elements. The integrated circuit of claim 21 wherein each said pass element comprises a pass gate having a pair of complementary transistors with their conduction paths coupled in parallel An integrated circuit as claimed in any one of claims 15 to 21 wherein said logic comprises one of: a processor; a digital signal processor; a microprocessor; and a video compression device. An integrated circuit as claimed in any one of claims 15 to 22 wherein said memory comprises one of a embedded memory, DRAM, SRAM, read only memory, FIFO, flash memory, EPROM and EEPROM. A computer comprising: an input device; an output device; and an integrated circuit coupled to said input device and said output device, said integrated circuit as claimed in any of claims 15 to 24.

Inventors: CHAN TSIU CHIU, ENG LAWRENCE P, CHAN, TSIU CHIU, ENG, LAWRENCE P.
Applicants: ST MICROELECTRONICS INC, STMICROELECTRONICS, INC.
Application year: 1997
Main classification: G11C29
IPC codes: G11C29, G06F11, G06F12, G06F15