Abstract:
An electronic device includes an Erasable Programmable Read-Only Memory (EPROM), a programmable logic device connected to the EPROM, and a single package enclosing the EPROM and the programmable logic device. The electronic device provides combined functionality that allows the EPROM to store configuration data for a programmable logic device, a Static Random Access Memory (SRAM), or an external programmable logic device, while the programmable logic device is configured to implement another function, such as a Joint Test Access Group interface function, an address decoder function, or a state machine function.

Description:
This application claims priority to the provisional patent application entitled: “Configuration EPROM with Programmable Logic”, Ser. No. 60/079,281, filed Mar. 25, 1998. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     This invention relates generally to Erasable Programmable Read-Only Memories (EPROMs) used to configure electronic devices, such as programmable logic devices or Static Random Access Memories (SRAMs). More particularly, this invention relates to a single package electronic device including both a programmable logic device and an EPROM. 
     BACKGROUND OF THE INVENTION 
     Erasable Programmable Read-Only Memories (EPROMs) are used to configure electronic devices, such as Static Random Access Memories (SRAMs) and programmable logic devices. In the case of SRAMs, the SRAM must be configured each time the system initializes. Generally, this initialization configuration is achieved by downloading data from an EPROM into the SRAM. Additionally, data may be transferred from the EPROM to the SRAM whenever new configuration data is needed. EPROMs are used in a similar manner when configuring programmable logic devices. 
     EPROMs are commonly used on a printed circuit board with other control circuits. Frequently, these control circuits operate in connection with programmable logic devices to which the EPROMs download configuration data. Since EPROMs and control circuits sometimes operate together it would be highly desirable to provide an EPROM that could perform both fundamental configuration functions and extended control functions. Such an approach could reduce the number of circuits on a printed circuit board, thereby saving space and otherwise reduce cost. 
     SUMMARY OF THE INVENTION 
     An electronic device includes an Erasable Programmable Read-Only Memory (EPROM), a programmable logic device connected to the EPROM, and a single package enclosing the EPROM and the programmable logic device. The electronic device provides combined functionality that allows the EPROM to store configuration data for an external programmable logic device, while the programmable logic device is configured to implement some other function, such as a Joint Test Access Group interface function, an address decoder function, or a state machine. 
     The device of the invention eliminates the need for discrete devices on a printed circuit board and therefore saves space on the printed circuit board. Further, the combined functional device of the invention is less expensive than the discrete device approach of the prior art. The invention also allows a user to make last minute changes to the configuration schemes without altering the layout of the printed circuit board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates an electronic device constructed in accordance with an embodiment of the invention. 
     FIG. 2 illustrates the electronic device of the invention being used in connection with a microprocessor and external programmable logic devices. 
     FIG. 3 illustrates the electronic device of the invention being used in an embedded system. 
     FIG. 4 illustrates the electronic device of the invention incorporated into a data processing system. 
     Like reference numerals refer to corresponding parts throughout the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an electronic device  20  constructed in accordance with an embodiment of the invention. Electronic device  20  includes a programmable logic device  22  and an EPROM  24  housed in a single package  26 . By way of example, programmable logic device  22  may be from the MAX 7000 Programmable Logic Device Family sold by Altera Corporation, San Jose, Calif., while the EPROM may be from the Configuration EPROMs for FLEX Devices sold by Altera Corporation, San Jose, Calif. Programmable logic device  22  and EPROM  24  may be on separate substrates or a single substrate. Interface paths  25  are formed between the programmable logic device  22  and the EPROM  24 . 
     As shown in FIG. 1, package  26  includes input/output pins  27 . Also, the package  26  has EPROM input pins  29  and EPROM output pins  30 . 
     In one embodiment of the invention, EPROM  24  is preprogrammed with data. Upon initialization of electronic device  20 , EPROM  24  uses interface paths  25  to send certain of the stored data to programmable logic device  22 . The data transferred from EPROM  24  may be used to configure programmable logic device  22 . Programmable logic device  22  could be a standard programmable logic device. 
     FIG. 2 illustrates electronic device  20  as a component of a system  31 . In FIG. 2, electronic device  20  is electrically connected to a microprocessor  33  and a set of external programmable logic devices  34  and  36 . External programmable logic devices  34  and  36  may be any programmable logic device, SRAM, Dynamic Random Access Memory, or the like. In one embodiment of the system of FIG. 2, programmable logic device  22  is configured as a decoder  22  and EPROM  24  stores configuration data for external programmable logic devices  34  and  36 . Decoder  22  allows microprocessor  33  to select a particular external programmable logic device by directing decoder  22  to send a signal accessing a particular address or providing a particular signal to an already selected address. 
     In one example of the operation of the system of FIG. 2, EPROM  24  is programmed with data. Upon initialization of the system, EPROM  24  may transfer certain of the data to decoder  22  thereby providing decoder  22  with configuration information. Additionally, EPROM  24  provides certain of its data to external programmable devices  34  and  36 . External programmable devices  34  and  36  may be selectively enabled according to the signals of decoder  22 . Microprocessor  33  may direct decoder  22  to send electronic signals, selectively enabling external programmable device  34  or  36 . 
     In yet another embodiment of the invention, programmable logic device  22  is a state machine. The interactions between the state machine  22 , EPROM  24 , microprocessor  33 , and external programmable logic devices  34  and  36  are analogous to the interactions described with respect to the previous embodiments of the invention. 
     In the prior art, a separate decoder or state machine and EPROM have been used to perform functions that are executed by the unitary device of the invention. Electronic device  20  simplifies the configuration process, reduces the number of devices on the printed circuit board, and also reduces system cost. 
     FIG. 3 illustrates device  20  of the invention positioned in an embedded system  40 , which includes an embedded microprocessor  42 . In one embodiment of the apparatus of FIG. 3, programmable logic device  22  is implemented as a JTAG interface circuit. JTAG external circuitry  44  interacts with programmable logic device  22 . JTAG external circuitry  44  is used to program and interact with the embedded system  40 , as appreciated by those skilled in the art. 
     FIG. 4 illustrates electronic device  20  of the present invention connected to a system bus  60  in a data processing system  50 . Data processing system  50  may include one or more of the following components: a microprocessor  52 , memory  54 , for example SRAM, input/output circuitry  56 , and peripheral devices  58 . These components are coupled together by a system bus  60  and are populated on a circuit board  62 , which is contained in an end-user system  64 . 
     Electronic device  20  can be implemented by itself or in a system, such as system  50 , to facilitate a wide variety of tasks, such as computer networking, data networking, instrumentation, video processing, digital signal processing, process monitoring, system failure detection, status indicator, data encryption, or any other application where the advantage of using reprogrammable logic and an EPROM is desirable. As demonstrated above, device  20  can be used to perform a variety of logic functions. Additional implementation examples include using device  20  as a processor or controller that works in cooperation with microprocessor  52 . Device  20  may also be used as an arbiter for arbitrating access to a shared resource in system  50 . In yet another example, device  20  can be configured as an interface between microprocessor  52  and one of the other components in system  50 . It should be noted that the foregoing examples including the implementation of electronic device  20  in system  50  is only exemplary, and that the true scope and spirit of the invention should be indicated by the claims. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. In other instances, well known circuits and devices are shown in block diagram form in order to avoid unnecessary distraction from the underlying invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following Claims and their equivalents.