Abstract: A system including a programmable logic device (PLD) mounted on a populated printed circuit board, and a configuration processor. The PLD includes a plurality of input/output blocks (IOBs), each having an input buffer and an output buffer. Each output buffer is coupled to an associated adjustable slew rate control circuit and to an adjustable delay line of the PLD. The configuration processor controls each of the slew rate control circuits to provide a first slew rate. The configuration processor also controls the output buffers to be coupled to the adjustable delay line. The configuration processor then controls the adjustable delay line to generate a first test pulse, which is applied to each of the output buffers. Depending on the impedances of the printed circuit board, the first test pulse transmitted from a particular output buffer may be reflected. Reflected test pulses return to the associated input buffers and are recorded.

Abstract: An integrated circuit combination includes a second piggy-back small integrated circuit chip mounted on the carrier of a first integrated circuit chip. The combination can be mounted on a board without requiring board space for interconnecting the first and second chips. The lid of the first chip is cut away so that the second chip can be mounted to the first without increasing the height of the combination over the height of the first chip. The two chips preferably comprise an FPGA and a PROM for programming the FPGA. The combination increases security as well as reducing board space because it is difficult to read a bitstream being transmitted from the PROM to the FPGA when the PROM is directly mounted on the FPGA.

Abstract: A method using replication of distributed arithmetic logic circuits and recursive interpolation of reduced angular increments of sine and cosine sum constants in logic look-up tables permits the computation of vector rotation and large FFTs in an efficient-parallel fashion within a unitary field programmable gate array chip, without off-chip memory for storing constants.

Abstract: One embodiment of the invention allows a designer to quickly and efficiently obtain a simulation model for a new integrated circuit implementation of a circuit design from the PLD simulation model for that circuit design. The designer begins with the simulation model of the PLD and back annotates the simulation model with timing characteristics from a target technology. The back annotation substitutes timing values in the PLD simulation model with timing values from the target technology to generate the new integrated circuit simulation model.

Abstract: A programming method of a programmable logic device (PLD) to enable system recovery after power failure is provided. Key configuration bits controlling output enable signals of the PLD are programmed at a different time than all other configuration bits in the PLD. If those key bits are unprogrammed, the PLD behaves identically to a fully erased device. Thus, by programming the key configuration bits after all other bits are successfully programmed, any potential damage to the system is virtually eliminated. In this manner, if the main programming sequence is interrupted, the PLD will power up with partial internal activity, but no active output signals. Moreover, even if the interruption occurs during the programming of these few bits, the result is only a partial activation of output signals which is significantly better than the activation of output signals with incorrect functions.

Abstract: The present invention provides a method and apparatus for combining tristate buffers into wide logic functions. The invention provides for an arbitrary number of drivers to be accommodated on a single line in a circuit wherein the number of tristate buffers coupled to the line is limited. A plurality of long lines are used to implement wired logic functions, and the lines are then combined to implement wired logic functions wider than can be accommodated by a single long line. In one embodiment, each of the long lines is coupled to an input of a CLB to combine the portions of the logic function into a whole function using a function generator. In another embodiment, the wired logic portions are combined by cascading the long lines into the tristate inputs of another long line. In yet another embodiment, the long lines are cascaded into another line such as an edge decoder to form a logic function.

Abstract: A field programmable gate array is provided which has a programmable portion and a dedicated controller-interface circuit. The programmable portion includes conventional input/output (I/O) blocks and configurable logic blocks (CLBs). The controller-interface circuit allows the FPGA to be operably coupled to an external computer bus, such as a PCI bus. The programmable portion and the controller-interface circuit are separately programmable. As a result, after the controller-interface circuit is initialized, the programmable portion can be cleared and reconfigured without having to re-initialize the controller-interface circuit. The programmable portion is programmed in accordance with an implied addressing scheme in response to a configuration bit stream.

Abstract: Described is a programmable logic device with on-chip configuration memory for controlling the state of various programming points. Each programming point includes two or more sequential memory elements, each of which may be programmed to include a data bit associated with a different circuit configuration. The state of an accessed one of the sequential memory elements (i.e., the bit of configuration data currently stored in that memory element) dictates the current FPGA configuration. Alternate configuration bits are stored in the remaining memory elements. The configuration of the FPGA may then be changed by sequentially shifting a data bit from one of the inactive memory cells into the active memory cell. In one embodiment the sequential memory cells are configured in a ring to support alternating between two or more configurations.

Abstract: Described is a user-controlled, variable-delay interconnect structure for a programmable logic device (PLD), and a method for using this structure. In accordance with the invention, the signal propagation delays for selected signal paths can be precisely adjusted either while the PLD is being programmed or while the PLD is operating as a logic device. The delays are adjusted by selectively connecting otherwise unused interconnect lines to the signal path to increase the capacitive load on the interconnect lines that define the signal path. The ability to control the load on selected signal paths advantageously enables a user to precisely match the signal propagation delays of two or more signal paths. In one embodiment, the loads of selected signal paths can be modified while the FPGA is operational.

Abstract: A power-on reset circuit responds to a power decrease of very short duration by using a delay circuit having a high threshold inverter which reliably detects a voltage as high as a standard threshold voltage as a low voltage when the power supply voltage again begins to increase. A very low current source provides current for driving the power-on reset circuit only when providing a power-on reset signal and draws no current during normal circuit operation.

Abstract: A reference ring oscillator circuit (RROC) is used to determine timing characteristics of a test interconnect structure in an integrated circuit. The RROC includes an odd number of inverters coupled together in a ring manner and has defined test segments at which a test interconnect can be loaded. Reference timing characteristics of the unloaded RROC are determined according to a calibration method including the steps of: (a) directly measuring signal propagation delay through each segment of the RROC; (b) modeling each test segment using an RC tree type reference circuit model having reference elements; (c) simulating the reference circuit model to provide a functional relationship between two reference capacitors; (d) defining upper and lower bounds for propagation delay through the test segment in terms of the reference elements; (e) determining values for the reference capacitor elements; and (f) measuring a reference frequency of oscillation of the unloaded RROC.

Abstract: A closed loop clock delay adjustment system measures the drift between the delay introduced by clock buffers and by delays inserted at the device data input pins. The system uses a reference delay at the input of a measurement flip-flop. The reference delay is defined to be an approximate average of the delays at the data input pins. An external clock signal is coupled to the input of the reference delay. The output of the reference delay is coupled to the data input of the measurement flip-flop. The external clock signal is also coupled to the input of a variable clock delay buffer sub-circuit. The output of the variable clock delay buffer is coupled to the clock signal input of the measurement flip-flop. In operation, the measurement flip-flop compares the variable clock delay buffer output signal with the clock signal delayed by the reference delay. If the variable clock delay buffer output signal is delayed more than the reference delay output signal, the variable clock delay is decreased.

Abstract: A method is described for measuring localized operating temperatures and voltages on an integrated circuit. The integrated circuit includes an oscillator circuit with a frequency that varies with temperature and/or applied voltage. The frequency of the oscillator is then determined, using a constant voltage, for a number of temperatures to establish a known relationship between oscillation frequency and temperature. Once the relationship is known, a similar oscillator is included within or adjacent a second circuit of the integrated circuit. The operating temperature or operating voltage of the second circuit may then be determined by monitoring the frequency of the oscillator while the second circuit is operational.

Abstract: A programmable logic device (PLD) which includes a phase comparator in addition to the conventional configurable logic circuitry normally present in the PLD. The configurable logic circuitry of the PLD includes a clock distribution circuit which is configured to route a clock signal VCO.sub.OUT generated by a voltage controlled oscillator (VCO) throughout the PLD as a distributed clock signal (DIST.sub.-- CLK). The DIST.sub.-- CLK signal is used to clock the output registers which route data values out of the PLD. The DIST.sub.-- CLK signal is also provided to the phase comparator. The phase comparator is also coupled to receive a clock signal CLK.sub.IN from an external device. In response, the phase comparator generates an error signal which is representative of the phase difference between the CLK.sub.IN and DIST.sub.-- CLK signals. This error signal is provided to a loop filter. In response, the loop filter generates a control signal, which in turn, controls the frequency of the VCO.sub.

Abstract: An improved method for concurrently programming in-system programmable logic devices (PLDs). More specifically, where within a plurality of serially connected PLDs, there are devices having different numbers of programmable memory cells, and devices whose memory cells require different wait periods to carry out programming, the method herein provides more optimum time efficiency and uses significantly less time overall for programming, erasing or reading back the PLDs. Also, the invention accommodates the implementation of retries to assure complete programming or erasing even when the initial attempt is not entirely successful. The method provides steps for accommodating PLDs with different wait times by bypassing fully programmed devices and speeding up programming times after smaller and slower devices are programmed and larger and faster devices are still not fully programmed.

Abstract: A memory cell array includes a first memory cell, a second memory cell, and a bit line which extends between the first and second memory cells. During normal operation, the bit line is used as a write path for data values to be written to the first and second memory cells. If the first memory cell is defective, the bit line is used to route the data value stored in the second memory cell to the first memory cell, effectively replacing the first memory cell with the second memory cell. In another embodiment, a memory cell array includes a first memory cell for storing a first data value and a second memory cell for storing a second data value. A first pair of bit lines are coupled to the first memory cell, and the first data value is written to the first memory cell on the first pair of bit lines. A second pair of bit lines are coupled to the second memory cell, and the second data value is written to the second memory cell on the second pair of bit lines.

Abstract: An apparatus for loading configuration information into a programmable integrated circuit (e.g., an FPGA) configurable to perform parallel loading or bit serial loading within the same architecture. The configuration information is presented to the FPGA in data frames of N serial bits each. Each data frame is divided into discrete serial portions having Y bits each (e.g., a data frame comprises N/Y portions). In parallel mode, the portions are loaded into a segmented configuration register, one portion per programming cycle, such that Y bits are loaded into the segmented configuration register in parallel. On each programming clock cycle during parallel loading, all the bits of a data frame portion are simultaneously loaded into the segments of the configuration register (at the first bit position for each segment) such that each segment receives one bit per programming cycle. The bits of the configuration register are then shifted down by one and the cycle repeats for the next data frame portion.

Abstract: An interactive graphical software tool is provided that can be used to report the configuration data (i.e., the state of the various configuration bits) in a programmed device as well as to probe and stimulate circuits in the programmed device. A graphical or textual representation of the configuration data can be displayed. When used with a programmable device having addressable flip-flops, such as a member of the Xilinx XC6200 family, one embodiment of the invention can change the state of any addressable flip-flop in the configured device. The graphical tool of the invention is preferably implemented using a high level programming language such as Java and features a graphical point and click user interface, remote access to hardware, and symbolic debug capability. According to another aspect of the invention, data can be written into a programmable device using an interactive software tool and a hardware device designed to interface with the programmable device.

Abstract: A programmable IC is provided that includes dedicated boundary scan logic having a programmable boundary scan bit-order. Boundary scan cells are provided, each cell being capable of providing the boundary scan functions associated with one I/O pad. In a mask programmable device, dedicated tracks are provided for adding mask programmable interconnect lines. In other programmable ICs such as FPGAs or PLDs, programmable interconnect lines are provided. In either case, the interconnect lines are used to implement the boundary scan data chain. Using these lines, the programmed device can "swap the order" of I/O cells in the boundary scan data chain, or leave cells out of the chain entirely. In one embodiment, the interconnect lines traverse each cell, programmably connecting the data inputs and outputs of adjacent or non-adjacent boundary scan cells.

Abstract: The notion of global signals (e.g., global set/reset and global tristate) is of significance to programmable logic user throughout the design process. Regardless of whether the HDL designer explicitly describes the use of a global signal, they are present in the implemented device since they are an integral part of the initialization and start-up process. This may lead to mismatches between the Register Transfer Level (RTL) simulation and the timing simulation. While a methodology for verifying the functionality of global signals is available for schematic design entry, none exists for HDL design tools. A verification method for HDL designers is disclosed providing access to all the functionality relating to global networks currently available to the schematic designers and allowing reuse of the testbench without losing HDL code portability.