Abstract: A clock routing circuit is coupled to receive a primary clock signal, a secondary clock signal, and a select signal, all of which may be asynchronous with respect to one another. When the select signal is in a first state, the clock routing circuit passes the primary clock signal as an output clock signal. When the select signal transitions to a second state, the clock routing circuit waits for the primary clock signal to transition in a predetermined direction (i.e., rising edge or falling edge). Upon detecting the transition of the primary clock signal, the clock routing circuit holds the state of the output clock signal. The clock routing circuit then waits for the secondary clock signal to transition in the predetermined direction. Upon detecting the transition of the secondary clock signal, the clock routing circuit passes the secondary clock signal as the output clock signal.

Abstract: A dedicated block random access memory (RAM) is provided for a programmable logic device (PLD), such as a field programmable gate array (FPGA). The block RAM includes a memory cell array and control logic that is configurable to select one of a plurality of write modes for accessing the memory cell array. In one embodiment, the write modes include a write with write-back mode, a write without write-back mode, and a read then write mode. The control logic selects the write mode in response to configuration bits stored in corresponding configuration memory cells of the PLD. The configuration bits are programmed during configuration of the PLD. In one variation, the control logic selects the write mode in response to user signals. In a particular embodiment, the block RAM is a dual-port memory having a first port and a second port. In this embodiment, the first and second ports can be independently configured to have different (or the same) write modes.

Abstract: A dedicated block random access memory (RAM) is provided for a programmable logic device (PLD), such as a field programmable gate array (FPGA). The block RAM includes a memory cell array and control logic that is configurable to select one of a plurality of parity or non-parity modes for accessing the memory cell array. In one embodiment, the non-parity modes include a 1×16384 mode, a 2×8192 mode, and a 4×4096 mode, while the parity modes include a 9×2048 mode, a 18×1024 mode and an 36×512 mode. The control logic selects the parity/non-parity mode in response to configuration bits stored in corresponding configuration memory cells of the PLD. The configuration bits are programmed during configuration of the PLD. In one variation, the control logic selects the parity/non-parity mode in response to user signals. In a particular embodiment, the block RAM is a dual-port memory having a first port and a second port.

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: An input/output interconnect (IOI) circuit is provided for coupling input/output (IO) blocks to an array of configurable logic tiles in a field programmable gate array (FPGA). Each of the tiles includes a configurable logic block and a programmable interconnect structure that includes a plurality of intermediate-length buses. The intermediate-length buses are staggered, such that only a subset of the intermediate-length buses routed by a logic block is connected to the logic block. The IOI circuit includes routing circuits at the perimeter of the array for terminating the intermediate-length buses. In one embodiment, the routing circuits connect various ends of unidirectional intermediate-length buses in a U-turn configuration, thereby making use of all of the intermediate-length buses, and maintaining a regular pattern of intermediate-length buses in the tiles.

Abstract: An FPGA configuration memory is divided into columnar frames each having a unique address. Configuration data is loaded into a configuration register, which transfers configuration data frame by frame in parallel. In a preferred embodiment, an input register, a shadow input register and a multiplexer array permit efficient configuration data transfer using a larger number of input bits than conventional FPGAs. A flexible external interface enables connection with bus sizes varying from a predetermined maximum width down to a selected fraction thereof. Configuration data transfer is made more efficient by using shadow registers to drive such data into memory cells on a frame-by-frame basis with a minimum of delay, and by employing a multiplexer array to exploit a wider configuration data transfer bus. The speed of configuration readback is made substantially equal to the rate of configuration data input by employing configuration register logic that supports bidirectional data transfer.

Abstract: A method for selecting the state assignments of a complex programmable logic device (CPLD) to minimize power consumption. Within the CPLD, a plurality of macrocells are selected to store a corresponding plurality of state variables, wherein the number of macrocells is selected to be equal to the number of states. For each of the states, one of the macrocells is assigned to store a state variable having a first logic state, and the remaining macrocells are assigned to store state variables having a second logic state. The macrocells storing state variables having the second logic state exhibit a lower power consumption than the macrocell storing the state variable having the first logic state. In addition, each of the macrocells includes a plurality of wired logic gates, each being in a high-current state or a low-current state. The number of wired logic gates in the low-current state is maximized in the macrocells assigned to store the state variables having the second logic state.

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: 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: Dynamic latches for writing to a synchronous RAM are controlled by a clock signal and a delay circuit so that the dynamic latches will not stay in a latched state for more than a selected time interval regardless of the clock signal. One delay circuit limits the length of a write enable signal. Another delay circuit responds to the write enable signal and after a delay returns the address and data latches to their transparent states.

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: The present invention provides a logic circuit that is programmable to implement a first logic function or a second logic function using as few as four transistors. In one embodiment, the logic circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, a first signal line for receiving a first input signal, a second signal line for receiving a second input signal, a control signal line for receiving a control signal, and an output signal line for receiving an output signal. The first transistor and the second transistor are connected in series between the control signal line and the output signal line. The third transistor is connected in series between the first input signal line and the output signal line. The fourth transistor is connected in series between the second input signal line and the output signal line.

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 nonfield 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. Moveover, 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: For a memory cell comprising a latch with cross-coupled inverters and an n-channel access transistor, the inverter that can contend with the access transistor is connected not between power and ground but between power and a transistor that disconnects the inverter from ground when the memory cell is being written. This allows transistors in the memory cell to be small and still function properly, without requiring that a port be provided for the complement of the data signal. The invention is important when there are several write ports to the memory cell and the addressing overhead is significant.

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.