Abstract: A programmable logic device having a plurality of gates which can be programmed to implement a plurality of product terms for representing logic functions, wherein an input signal is processed according to the logic functions, and a resulting output signal is generated having a selectable output voltage level. A desired output voltage level is specified. A generator supplies the desired output voltage to an output buffer of the programmable logic device. This generator may operate independently from the generator used to supply power to the programmable logic device. The processed signal drives the output buffer, and the output signal from the output buffer corresponds to the desired output voltage.

Abstract: A zero power circuit includes an upper power supply voltage pad, battery pad, a power control circuit, and a suppression circuit. The power control circuit provides power to the zero power circuit by switching between the battery pad and the upper power supply voltage pad. The suppression circuit is connected in series between the power control circuit and the battery pad. The suppression circuit includes a resistor connected in series between the battery pad and the power control circuit, wherein current flowing through the transistor during a latch condition causes the voltage to drop across the resistor, suppressing the latchup condition to the battery pad. The suppression circuit also includes a transistor connected in parallel with the resistor, the transistor having a gate, wherein a first signal applied to the gate turns off the transistor and a second signal applied to the gate turns on the transistor, wherein the resistor is shorted when the transistor is turned on.

Abstract: A deterministic method and apparatus for defining the size and switch assignments of a switch matrix. The method operates on a switch matrix having a number of inputs (N) and a number of outputs (M). When constructing the switch matrix, there will be M columns in the matrix. The method determines a minimum number of rows (R) for the switch matrix. The resultant general purpose R.times.M switch matrix allows any combination of a subset of the N inputs, with up to M members, to be assigned to the outputs. The resultant R.times.M switch matrix will be smaller than an N.times.M switch matrix.

Abstract: A programmable logic circuit having a routing matrix capable of providing 100% connectability and routability of a plurality of input signals to their appropriate configuration function blocks. In the present invention, input signals are first routed through the routing matrix before being processed by the input buffers. Thus, a slow user signal is processed by the relatively slow routing matrix before being provided with increased drive by the input buffers and passed on to the faster logical blocks. A number of programmable control bits are stored in SRAM. These control bits are decoded to determine which of the transmission gates of the routing matrix should be enabled. In this manner the input signal is routed to the appropriate configuration function block. Following the routing matrix is the input buffer. The highly driven output signal from the buffer is then passed to the configuration function block which performs the programmed logic functions on the signal.

Abstract: A product term allocation arrangement in which each of a first plurality of input conductors may be programmably joined to a first plurality of output conductors and to a first plurality of AND gates, a second plurality of input conductors may be programmably joined to a second plurality of output conductors and to a second plurality of AND gates, apparatus which may be selected to perform either an AND or an OR function connected to receive input signals from one of the first plurality of AND gates and one of the second plurality of AND gates, and a plurality of OR gates connected to receive input signals from a selected number of the apparatus connected to receive input signals from one of the first plurality of AND gates and one of the second plurality of AND gates.

Abstract: A programmable logic device having the capability of initializing and resetting to a specified digital state. One or more clear/preset product terms are available for initializing and resetting the macrocells of the programmable logic device. Each macrocell can be either cleared to a "0" or preset to a "1" according to the clear/preset product terms. Control bits are used to select which of the clear/preset product terms, if any, are to be used to clear and/or preset a particular macrocell. These control bits are programmable for each of the macrocells, thereby allowing each macrocell to output either a "0" or a "1", as desired by the user, independent of the other macrocells. The macrocells can be cleared and preset asynchronously.

Abstract: A specialized output buffer circuit which obviates the need to utilize a separate multiplexer to determine polarity selection and output type selection in a programmable logic device is disclosed. In accordance with the present invention, these determinations are made in a specialized output buffer circuit. A sum of product term, a complement of the sum of product term, a registered version of the sum of product term, and a complement of the registered version of the sum of product term, are coupled directly to the output buffer circuit, wherein one of these signals is selected and coupled to an output pin.

Abstract: In a programmable logic device having a plurality of gates capable of being programmed according to a plurality of product terms representing logic functions, an apparatus for allocating the product terms to a plurality of outputs. A first set of product terms are steerable to one of at least two outputs. A second set of product terms is permanently assigned to a predetermined output. The second set is comprised of more product terms than the first set, wherein the average number of product terms per output is low, yet a user has the flexibility of implementing logic functions requiring a relatively large number of product terms.

Abstract: A programmable gate array comprised of a number of configurable functional blocks. Each configurable functional block has a number (m) of inputs. A global interconnect matrix interconnects the configurable functional blocks. The global interconnect matrix provides for routing any combination of signals entering the matrix to any configurable functional block, up to and including the maximum number (m) of inputs of a configurable functional block. Each configurable functional block includes a product term array connected to the m inputs. The product term array can perform a logical AND of up to m bits. A compare term array is also connected to the m inputs. The compare term array can perform an identity compare of up to m/2 bits. A number n of macro cells are provided in each configurable functional block wherein the number n is less that the number m.

Abstract: An integrated circuit having a normal operating mode and a special operating mode, such as a special test mode, is disclosed. The special test mode is enabled by a series of signals, such as overvoltage excursions at a terminal, rather than by a single such excursion, so that it is less likely that the special test mode is entered inadvertently, such as due to noise or power-down and power-up of the device. The circuit for enabling the test mode includes a series of D-type flip-flops, each of which are clocked upon detection of the overvoltage condition together with a particular logic level applied at another terminal; multiple series of flip-flops may be provided for multiple special test modes. Additional features include the provision of a power-on reset circuit which locks out the entry into the test mode during power-up of the device.

Abstract: An EEPROM cell suitable for use in programmable logic devices contains three transistors. A floating gate transistor is used to retain a programmed value using charge storage on the floating gate. A read transistor is connected between the floating gate transistor and an output signal line, and used to access the value stored in the floating gate transistor. A write transistor is connected to the floating gate transistor opposite the read transistor, and is used when programming the floating gate transistor. The write transistor and its associated control circuitry are fabricated to handle the higher programming voltages required by the floating gate device. The read transistor and associated drive circuitry are not required to handle the higher programming voltages, and can be fabricated using smaller, faster devices.

Abstract: A shift register used to shift programming and test data into a programmable logic device is modified so that each bit thereof can be directly set or reset. Control signals can be used to directly place the required test patterns into the shift register. A memory connected to the shift register, and associated logic, provides a means for testing whether data was accurately written to the array without shifting any data off of the device.

Abstract: A programmable cell for use in programmable logic devices utilizes CMOS SRAM technology. True and complement cells are paired, and generate a signal which can be combined with other such signals to give a product term. SRAM bits store program information, and drive the generated signal as a function of values at its true and complementary inputs. The generated signal goes through a full CMOS voltage swing, so that no sense amplifiers are required for the product term.

Abstract: An integrated circuit having a normal operating mode and a special operating mode, such as a special test mode, is disclosed. The special test mode is enabled by a series of signals, such as overvoltage excursions at a terminal, rather than by a single such excursion, so that it is less likely that the special test mode is entered inadvertently, such as due to noise or power-down and power-up of the device. The circuit for enabling the test mode includes a series of D-type flip-flops, each of which are clocked upon detection of the overvoltage condition together with a particular logic level applied at another terminal; multiple series of flip-flops may be provided for multiple special test modes. Additional features include the provision of a power-on reset circuit which locks out the entry into the test mode during power-up of the device.

Abstract: An integrated circuit having a normal operating mode and a special operating mode, such as a special test mode, is disclosed. The special test mode is enabled by a series of signals, such as overvoltage excursions at a terminal, rather than by a single such excursion, so that it is less likely that the special test mode is entered inadvertently, such as due to noise or power-down and power-up of the device. The circuit for enabling the test mode includes a series of D-type flip-flops, each of which are clocked upon detection of the overvoltage condition together with a particular logic level applied at another terminal; multiple series of flip-flops may be provided for multiple special test modes. Additional features include the provision of a power-on reset circuit which locks out the entry into the test mode during power-up of the device.

Abstract: A standard logic block, or macrocell, is provided for use on programmable logic devices. The macrocell uses RAM to perform logic functions, and further includes circuitry which allows writing of data to the RAM during use. Each logic block can be configured at programming time to be either a user RAM, allowing the user to write data to such memory during use, or configured as performing logic functions. The contents of macrocells configured as providing logic functions cannot be changed except by reprogramming the device.

Abstract: A programmable logic integrated circuit device utilizes volatile memory elements such as SRAM for retaining configuration information. A circuit is provided as part of the device for detecting loss of power on a supply input pin. When power loss is detected, a backup voltage supply, packaged with the programmable logic device as a unit, is connected thereto. The backup power is used to supply voltage only to those portions of the device having volatile memory elements containing configuration information. Backup power is not provided to input and output buffers of the device, thereby preventing excess loads being placed upon the backup device because of events which may occur external to the programmable logic device.

Abstract: According to the present invention, during programming of a programmable logic device, programming information corresponding to an input signal is loaded into a shift register. This input information is compared with programming information corresponding to a second, complementary input signal to determine if the two signals are used by the programmable logic device. If the two inputs are not used, a bit is stored in a memory cell indicating such nonuse. An input buffer is disabled when the bit in the memory cell indicates the complementary signals corresponding to that input buffer are not used.

Abstract: A standard logic block, or macrocell, is provided for use on programmable logic devices. The macrocell uses RAM to perform logic functions, and further includes circuitry which allows writing of data to the RAM during use. Each logic block can be configured at programming time to be either a user RAM, allowing the user to write data to such memory during use, or configured as performing logic functions. The contents of macrocells configured as providing logic functions cannot be charged except by reprogramming the device.

Abstract: A programmable logic integrated circuit device utilizes volatile memory elements such as SRAM for retaining configuration information. A circuit is provided as part of the device for detecting loss of power on a supply input pin. When power loss is detected, a backup voltage supply, packaged with the programmable logic device as a unit, is connected thereto. The backup power is used to supply voltage only to those portions of the device having volatile memory elements containing configuration information. Backup power is not provided to input and output buffers of the device, thereby preventing excess loads being placed upon the backup device because of events which may occur external to the programmable logic device.