Abstract: The present invention allows one portion of an FPGA to reconfigure another portion of the same FPGA. The invention makes use of input/output ports that can be connected on the input side to a frame register for loading configuration data into the FPGA. When a portion of the FPGA is to be reconfigured, data are loaded by a portion of the FPGA not being reconfigured into the frame register of the FPGA and addressed to the portion of the FPGA being reconfigured. Loading of the data is accomplished by forming a configuration data stream in the portion of the FPGA not being reconfigured, then applying the configuration data stream to an output buffer of the FPGA and forwarding that data to an input buffer that is connected to a frame register of the FPGA configuration structure.

Abstract: A carry logic circuit is provided for an array of configurable logic blocks (CLBs), wherein each configurable logic block includes an array of logic cells arranged in rows and columns. At least one column of logic cells includes a carry output signal selection circuit. At least one other column of logic cells includes a carry initialization circuit. The locations of the carry output signal selection circuits and carry initialization circuits are identical in each of the CLBs, and the CLBs have identical first columns of configurable logic cells and identical second columns of configurable logic cells. Dedicated routing circuitry is provided for column shifting the carry chains between vertically adjacent CLBs. Column shifting is performed such that a column of logic cells in one CLB is coupled to a non-corresponding column of logic cells in a vertically adjacent CLB.

Abstract: In an FPGA having a tristate bus structure formed by a multiplexer chain extending across a plurality of logic units, a programmable function generator is provided to interface between the input and enable signal lines of logic units and the corresponding multiplexer's input and control terminals and is coupled to receive a mode control signal. When the mode control signal is in a first logic state, the function generator couples the input and enable signals to the corresponding multiplexer input and control terminals to emulate a tristate input bus. When the mode control signal is in a second logic state, the function generator receives first and second data signals from corresponding input and enable lines. In response thereto, the function generator couples one of the data signals to the corresponding multiplexer input terminal and provides an exclusive-OR logic function of the first and second data signals to the corresponding multiplexer control terminal.

Abstract: A programmable logic device, such as a field programmable gate array (FPGA) which includes an array of configurable logic elements (CLEs) and a corresponding array of multiplier tiles. The CLEs can be operated as conventional configurable logic elements, completely disconnected from the array of multiplier tiles. However, selected CLEs can also be coupled to selected multiplier tiles, thereby creating a relatively high density multiplier circuit. Each of the multiplier tiles includes a multiplier array having a predetermined size (e.g., a 2.times.4 bit multiplier array). The multiplier tiles can be selectively coupled to one another, such that the multiplier arrays are connected to form a relatively large multiplier circuit. The desired multiplier and multiplicand bits are routed into the multiplier tiles from associated CLEs. Similarly, the resulting product bits are routed from the multiplier tiles to associated CLEs.

Abstract: A field programmable gate array (FPGA) which includes first and second arrays of configurable logic blocks, and first and second configuration cache memories coupled to the first and second arrays of configurable logic blocks, respectively. The first configuration cache memory array can either store values for reconfiguring the first array of configurable logic blocks, or operate as a RAM. Similarly, the second configuration cache array can either store values for reconfiguring the second array of configurable logic blocks, or operate as a RAM. The first configuration cache memory array and the second configuration cache memory array are independently controlled, such that partial reconfiguration of the FPGA can be accomplished. In addition, the second configuration cache memory array can store values for reconfiguring the first (rather than the second) array of configurable logic blocks, thereby providing a second-level reconfiguration cache memory.

Abstract: The invention provides an FPGA comprising an array of identical tiles. Each tile comprises a logic block that includes a Configurable Logic Element (CLE). In one embodiment, the CLE is implemented in two similar portions called "slices". Each slice has a separate carry chain. In a CLE with four function generators, each carry chain incorporates the outputs of two function generators.

Abstract: A field programmable gate array (FPGA) which includes first and second arrays of configurable logic blocks, and first and second configuration cache memories coupled to the first and second arrays of configurable logic blocks, respectively. The first configuration cache memory array can either store values for reconfiguring the first array of configurable logic blocks, or operate as a RAM. Similarly, the second configuration cache array can either store values for reconfiguring the second array of configurable logic blocks, or operate as a RAM. The first configuration cache memory array and the second configuration cache memory array are independently controlled, such that partial reconfiguration of the FPGA can be accomplished. In addition, the second configuration cache memory array can store values for reconfiguring the first (rather than the second) array of configurable logic blocks, thereby providing a second-level reconfiguration cache memory.

Abstract: A field programmable gate array (FPGA) having a plurality of configurable logic blocks (CLBs). Each of the CLBs includes programmable interconnect resources, a field programmable configurable logic element (CLE) circuit and a corresponding non-field programmable gate array. The programmable interconnect resources are programmed to selectively couple or decouple each CLE circuit from its corresponding non-field programmable gate array. Dedicated interconnect resources enable adjacent non-field programmable gate arrays to be coupled. By coupling adjacent non-field programmable gate arrays, one or more relatively large non-field programmable gate arrays can be formed. The non-field programmable gate arrays have a greater logic density than the CLE circuits, thereby providing an improved logic density to the CLBs. Moreover, because each CLB includes a non-field programmable gate array, each of the CLE circuits is readily connectable to a non-field programmable gate array.

Abstract: A clock distribution circuit and method for programmable ICs whereby the incoming clock frequency is optionally divided by two and distributed at the new, lower frequency. Programmable dual-edge/single-edge flip-flops are provided that optionally operate at twice the frequency of the distributed clock, being responsive to both rising and falling edges of the distributed clock. When the clock divider is enabled and the flip-flops are programmed as dual-edge, the operating frequency is the same as that of the incoming clock; however, the frequency of the distributed clock is reduced by one-half. This reduction halves the frequency at which the clock distribution circuits operate, and consequently approximately halves the power dissipated by the clock distribution circuit, thereby providing a programmable power-saving mode.

Abstract: A user-defined logic device, such as a field programmable gate array (FPGA), having a dedicated internal bus, a plurality of dedicated bus interface circuits, and a programmable logic array. The dedicated bus interface circuits are connected in parallel to the dedicated internal bus. The programmable logic array is programmable to implement one or more functions. The programmable logic array is coupled to the dedicated bus interface circuits, such that each function is coupled to a corresponding bus interface circuit. The functions can communicate with one another through the bus interface circuits and internal bus, or through communication pathways located within the programmable logic array. In addition, the functions can communicate with devices external to the user-defined logic device through a bus bridge circuit which is coupled to the dedicated internal bus, or directly through the pins of the user-defined logic device.

Abstract: A field programmable gate array (FPGA) having an array of configuration memory cells arranged in rows and columns. The configuration memory cells store configuration data values for configuring the FPGA. Each configuration memory cell is coupled to a corresponding row line through a corresponding cell access transistor. A row access circuit is coupled to the row lines. To re-program a first set (but not a second set) of configuration memory cells in a column, the row access circuit initially pre-charges each of the row lines, and then provides configuration data values on a first set (but not a second set) of the row lines. All cell access transistors in the column are coupled to a column select line. To avoid losing data in any memory cell, a relatively low read voltage, followed by a higher write voltage, is applied to the column select line. When the read voltage is applied to the column select line, the associated cell access transistors are weakly turned on.

Abstract: A method for controlling the operation of an FPGA. Initially, a function generator of the FPGA is configured as a ROM look up table which holds a first set of data values. These data values are selectively routed to an output terminal of the function generator in response to a plurality of input signals which are provided to the function generator. The first set of data values is selected to define a first function implemented by the function generator. Subsequently, the function generator is reconfigured as a user RAM, thereby enabling a second set of data values to be written to the function generator. The function generator is then reconfigured as a ROM look up table which holds the second set of data values. These data values are selectively routed to the output terminal of the function generator in response to the input signals provided the function generator. The second set of data values is selected to define a second function implemented by the function generator.

Abstract: A field programmable gate array (FPGA) having an array of configurable logic blocks (CLBs) which can be partially reconfigured. Each column of CLBs is connected to a corresponding column select line, and each row of CLBs is connected to a corresponding row select line. A rectangular set of CLBs to be reconfigured is selected, wherein the rectangular set of CLBs is defined by the intersection of one or more consecutive columns of CLBs and one or more consecutive rows of CLBs. Column select signals are asserted on the column select lines associated with the one or more consecutive columns of CLBs. Similarly, row select signals are asserted on the row select lines associated with the one or more consecutive rows of CLBs. CLBs which receive both an asserted column select signal and an asserted row select signal are enabled for reconfiguration.

Abstract: A chip includes a programmable logic device and a microprocessor, wherein at least one of the associated registers of the microprocessor is distributed in the programmable logic device. The distributed register is coupled to both the microprocessor and the programmable logic device. In this manner, the microprocessor has the ability to access the register and place a value into the programmable logic device all in one clock cycle. Additionally, the logic functions in the programmable logic device are also advantageously available to the microprocessor.

Abstract: A configurable logic block (CLB) which includes a function generator, carry logic and a first multiplexer. To operate the CLB as a multiplier, the function generator and the carry logic are each coupled to receive a first multiplier bit, a second multiplier bit and a carry signal. The function generator and carry logic are configured to provide a sum signal and a carry signal, respectively, in response to these input signals. The first multiplexer is coupled to receive the sum signal, the first multiplier bit, the second multiplier bit and a logic zero signal. The first multiplexer is controlled to pass a selected one of these signals in response to a first multiplicand bit and a second multiplicand bit. As a result, the CLB effectively creates and adds the partial products which result from multiplying the first and second multiplier bits and the first and second multiplicand bits.

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: 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: The invention provides an FPGA interconnect structure preferably included in an array of identical tiles. Each tile comprises a logic block that includes a Configurable Logic Element (CLE) and an output multiplexer. Fast feedback paths are provided within the logic block to connect the CLE outputs to the CLE inputs, either directly or through an input multiplexer. The fast feedback paths bypass the output multiplexer and therefore provide faster feedback than can be obtained in most conventional FPGA logic blocks. In one embodiment, the fast feedback paths provide the ability for all function generators in one CLE to drive each other through fast feedback paths, regardless of how logic is mapped into the function generators of the CLE.

Abstract: A memory system having a dual port first in, first out (FIFO) memory which performs read operations in synchronism with a read clock signal and write operations in synchronism with a write clock signal. The read clock signal is asynchronous with respect to the write clock signal. A synchronizing engine is provided to synchronize a current write address with the read clock signal, thereby creating a synchronized write address. The synchronizing engine further synchronizes a current read address with the write clock signal, thereby creating a synchronized read address. The synchronized write address is compared to the current read address to determine if a FIFO empty condition exists. Similarly, the synchronized read address is compared to the current write address to determine if a FIFO full condition exists.

Abstract: A carry logic circuit for a field programmable gate array (FPGA) which allows a carry input signal to be propagated through the carry logic circuit without passing through a multiplexer of another series connected circuit element. The carry logic circuit uses a function generator of the FPGA to provide a propagate signal in response to first and second input signals provided to the carry logic circuit. Also described are methods for performing a carry logic function in an FPGA.