Abstract: An ESD protection circuit combines a split bipolar transistor with a transistor layout which exhibits very high tolerance to ESD events. The split bipolar transistor divides current among many segments and prevents the current hogging which often causes an ESD failure. Several splitting structures are disclosed, each combining a resistor in series with each segment to distribute current evenly. The transistor takes advantage of the snap-back effect to increase current carrying capacity. Layout positions metal contacts away from regions of highest energy dissipation. Layout also allows high currents to be dissipated through ESD protection structures and not through circuit devices such as output drivers or through parasitic bipolar transistors not designed for high current. Sharp changes in electron density are avoided by the use of high-diffusing phosphorus in N-regions implanted to both lightly and heavily doped levels. Critical corners are rounded rather than sharp.

Abstract: A method and structure for verifying interconnect structure of an FPGA device after programming. In a preferred embodiment, after programming, a single wire segment on each net of a layout is pulled down to a low reference voltage. Voltage levels on all wire segments of the device are then captured and shifted out of the device for comparison to the expected values. Low voltage levels on segments expected to remain high reveal short circuit flaws. High voltage levels on segments expected to remain low reveal open circuit flaws.

Abstract: A method of state splitting in a state machine includes determining a number N of logic levels, i.e. CLB levels, for each state in a state machine. Number N is equal to N.sub.i-1 +log.sub.k f.sub.i wherein "k" is the number of input lines to a CLB, "i" is a particular node in a particular hierarchial level in the Boolean logic, and "f" is the number of fanin transitions to the particular node. An average number N(AV) as well as a maximum number N(MAX) of CLBs to implement the states in the state machine are also determined. Then, predetermined exit criteria are checked. One exit criterion includes determining that the maximum number N(MAX) is not associated with a state register, but is instead associated with an output, for example. Another exit criterion includes providing a ratio by dividing the maximum number N(MAX) by the average number N(AV). If the ratio is less than or equal to a split-factor, then this exit criterion is met. In one embodiment, the split factor is between 1.5 and 2.0.

Abstract: In an EPLD, a feedback switching circuit is provided on a feedback line connected between a macrocell output line and a interconnect matrix wordline, the switching circuit including a memory element and a switch for passing a macrocell output signal from the output line to the interconnect matrix wordline when the memory element is in a first state, and for blocking the macrocell output signal when the memory element is in a second state. This prevents coupling noise in the interconnect matrix because unnecessary feedback signals are prevented from entering the interconnect matrix. In another embodiment, a method is provided in which unused macrocells produce counteractive switching signals in the interconnect matrix to reduce the coupling effect caused by a multiple concurrent switching event. In another embodiment, a sense amplifier is provided in which an EPROM shields coupling between wordlines and bitlines in an interconnect matrix.

Abstract: A system and method for entering a circuit design into a computer using a schematic capture package. The schematic capture package is modified to include a library of state flow components represented by symbols which can be connected to produce a desired representation of the circuit design. The system allows a circuit design to be displayed on a video terminal using both state flow diagram and the schematic diagram symbols, with terminals of the state flow symbols connecting to terminals of the schematic symbols. The state flow diagram using state flow symbols is combined with a schematic diagram including schematic symbols to generate a netlist representing the combined circuit.

Abstract: A configurable cellular array is provided having a 2-dimensional array of cells in which each cell in the array has at least one input and output connection at least one bit wide to its neighbours. Each cell also has a programmable routing circuit to permit intercellular connections to be made. In one arrangement each cell contains a programmable function unit which includes a plurality of multiplexers. In a preferred arrangement the function unit and routing unit are programmable using associated Random Access Memory (RAM) areas within the cell. Each cell may be coupled to at least one global or array-crossing-signals so that all cells can be signalled simultaneously. The 2-dimensional array is rectangular and the intercell connections are orthogonal and are one bit wide.

Abstract: A method for programming a programmable logic device (FPLD) to implement a circuit design using a library of elements made up of general logic functions and an invert function. The general logic functions represent groups of the 2.sup.n.spsp.n specific logic functions which can be stored in an n-input lookup table addressing 2.sup.n data signals. The specific logic functions of each group differ by one or more inverted input signals and/or an inverted output signal. The method includes the step of technology mapping the circuit design using the library of elements. The general logic functions are assigned a finite value and the invert function is assigned a zero cost (or a very small cost). A subcircuit of the circuit design having n input signals (or less) and one output will always match one logic element from this library.

Abstract: A programmable logic array, where the programmable AND gate array in each block of macrocells conventionally generates a number of product terms to drive the macrocells in that block. Five product terms are assigned to each macrocell and are logically NORed together with two adjacent macrocell signals. The resultant signal drives the D terminal of the flip-flop in the macrocell. Independently, all five product terms are logically NORed together and the resultant signal is provided as an export signal to an adjacent macrocell for an additional product term use. Thirdly, each one of the product terms can be individually set as a separate private product term for use internally in that macrocell to replace the otherwise global provisions of internal macrocell signals such as set, reset, clock, output enable and inversion.

Abstract: A method and structure for providing ESD protection for Silicon-On-Insulator (SOI) integrated circuits. The ESD protection circuit includes an electrically conductive pad and first conductor segment fabricated over an insulating layer. The first conductor segment connects the pad directly to a first node, without an intervening input resistor. A first diode is fabricated over the insulating layer and connected between the first node and a first voltage supply rail. Similarly, a second diode is fabricated over the insulating layer and connected between the first node and a second voltage supply rail. Ballast resistors can be included in series with each of the diodes. A cross power supply clamp, also fabricated over the insulating layer, is connected between the first and second voltage supply rails. The first node of the ESD protection circuit is coupled to the SOI integrated circuit to be protected.

Abstract: A data-cascading hierarchically arranged electrically configurable logic device (ECD) system and an enable-cascading hierarchically arranged ECD system are provided. In both cases, the configuration bitstream includes a local count and at least one remainder count for each ECD. The local count determines the amount of configuration data to be stored locally. By setting this count to zero, an ECD can be bypassed. The remainder count determines the amount of data to be stored by devices down one hierarchical branch from the local ECD. By setting this count to zero, this branch can be bypassed and ECDs of a second branch can be configured sooner. In the data cascading system, the counts determine how data is routed through the ECDs. In the enable cascading system, the data is broadcast to all ECDs. The counts determine when and if the configuration enable inputs of downstream ECDs are to be activated.

Abstract: An input interface circuit for a logic device having a configuration of pull-up and pull-down devices for defining the logic level based on an undriven input signal where the pull-up and pull-down devices are independently and separately programmable to follow the input signal (e.g., a keeper circuit), or follow the inverse of the input signal, or programmed permanently on, or programmed permanently off. The interface circuit can be used to provide a known and programmable output signal for an IC input (or internal line) that does not have a known driving source. By allowing this degree of flexibility, the input interface circuit of the present invention, under programmed control, generates an output signal with positive or negative feedback based on the input signal; or the input interface circuit provides a constant high or constant low signal output, or can oscillate or provide a high impedance response as output.

Abstract: A PLD is operable in a variety of modes. In a first mode, the timeshare mode, the PLD remains at a single configuration for a plurality of user clock cycles. In a second mode, the logic engine mode, the PLD sequences through multiple configurations for each user cycle. In this mode, the period of time during which a configuration is active is called a micro cycle. In a third mode, the static mode, multiple configurations are programmed identically, so that the PLD performs the same function regardless of the configuration. Finally, the PLD is also operable in a combination mode, wherein part of the chip operates in one mode, for example, the static mode, and another part of the chip operates in the logic engine mode or the timeshare mode. In an alternative or co-existing embodiment, the PLD operates in one configuration mode during at least one user cycle and in another configuration mode during at least another user cycle.

Abstract: In an FPGA having registers which are part of a user's logic functions and a configuration memory which is read and written through an addressing structure, a register protect circuit controllably protects the contects of these user logic registers from being modified by signals from the user's logic, allows these registers to be written by a microprocessor through the configuration memory addressing structure, and allows both the user's registers and lines which provide combinational signals to be read by a microprocessor through the configuration memory addressing structure.

Abstract: A programmable single buffered six transistor switch box is provided. A six transistor switch box acts as a programmable junction between four intersecting lines. The switch box allows any two of the lines to be programmably interconnected to form a signal channel. Alternatively, two sets of the four lines can also be programmably interconnected so that two signal channels are formed. The present invention modifies the known six transistor switch box so that one line output from the switch box can be programmably buffered. By buffering the output signal, delay introduced by resistance and capacitance of the transistors switch box is significantly reduced. For short line lengths, the buffer delay can be greater than the delay associated with the resistance and capacitance of the transistors of the switch box. In these cases, the output is not buffered and the buffer is programmably bypassed.

Abstract: The present invention provides a means and method of generating a long error checking polynomial remainder having the ability to detect errors with high reliability and inserting only a subset of the polynomial remainder periodically into a data stream, then at the receiving end recalculating the polynomial remainder and checking the inserted subset for errors. The polynomial has the property that the current remainder value is a function of all data previously transmitted in a transmission session. The subset transmitted also preferably has this property. A longer subset of the polynomial remainder, or the full polynomial remainder, may be inserted less frequently, and is preferably sent and tested at the end of the transmission session. Both serial and parallel data streams may be checked.

Abstract: A input/output circuit (IOB) within an integrated circuit (IC) device, the output signal driving circuitry of the input/output device contains a dedicated multiplexer on the output path wherein a first and second output signal can be time multiplexed on a single output pad. The multiplexer can also be configured to perform as a high speed gate to realize AND, OR, XOR, and XNOR functions. Within an input/output circuit of a programmable integrated circuit, the system provides a dedicated multiplexer that can select between one of two output signals for sending over the single output pad of the IC device. In lieu of using a programmable memory cell as the select control for the dedicated multiplexer, the system allows a number of lines, including an output clock signal, to be the select control. By using the output clock as the select control, the data signals can be effectively time multiplexed over a single output pad and referenced by the output clock.

Abstract: A method of eliminating signal contention during reconfiguration of a programmable logic device includes the steps of: arranging a plurality of memory cells in sets and selectively programing the memory cells one set at a time, either in a first direction or a second direction. A structure for providing that selective programming includes a plurality of synchronous flip-flops, and a plurality of associated two-input multiplexers. A control signal in a first logic state provided to the multiplexers provides a first signal propagation direction through the flip-flops, whereas the control signal in a second logic state provides a second signal propagation direction through the flip-flops.

Abstract: A configurable multi-directional buffer circuit for a programmable integrated circuit. The novel buffer circuit is a configurable multi-directional buffer circuit having one pair of inverters and having a first input/output line and a second input/output line and a third input line multiplexed with the first input/output line. The novel buffer circuit is configurable to allow a signal from the first input/output line to be driven over the second input/output line or configurable to allow a signal from the second input/output line to be driven over the first input/output line. The novel buffer circuit also allows a signal over the third input line to be driven over the second input/output line. In either case, only a single pair of inverter circuits are used. In an alternate embodiment, the novel buffer allows signal over a fourth input line to be driven over the first input/output line.

Abstract: A programmable logic device (PLD) includes at least one configurable element, a plurality of programmable logic elements for configuring the configurable element(s), and a sequencer coupled to the plurality of programmable logic elements. Each programmable logic element typically includes a plurality of memory cells, wherein the sequencer accesses one of the plurality of memory cells during one step in a sequence of steps, each step initiated by one or more trigger signals. If the sequencer receives a plurality of trigger signals simultaneously, then the sequencer prioritizes these signals. Generally, each step provides one configuration of the PLD. In one embodiment, the sequence of steps includes less than all configurations of the PLD. In another embodiment, one trigger signal initiates a plurality of sequences of configurations.

Abstract: A plurality of DRAM cells are used to store the state of the programmable points in the FPGA ("FPGA DRAM cells"). A shadow DRAM array holds duplicate data of the plurality of DRAM cells. A DRAM cell of the shadow DRAM array is sensed during a refresh cycle. In this manner the refresh cycle does not alter the logic configuration of its associated FPGA DRAM cell.