Abstract: A 2/N mode clock generator that generates bus clock signals through the use of bus clock enable signals selecting bus clock pulses that are in phase and out of phase with a core clock signal. The clock generator maintains synchronization between the bus clock signal and the core clock signal so that they are always in a predetermined phase relationship.

Abstract: An apparatus and method for controlling and rectifying possible metastability situations having a first circuit with a first clock signal (CLOCK1) at a first clock rate and a second circuit with a second clock signal (CLOCK2) at a second clock rate, the second circuit having an input circuit coupled to the first circuit and receiving signals therefrom. A control circuit for controlling possible metastability situations arising in communication between the first circuit and the second circuit is also provided. The control circuit receives as input the first clock signal and the second clock signal and provides a shifting of at least one of the two clock signals, in such a way that a possible metastable state of the input circuit is avoided.

Abstract: A phase detection signal is generated with a phase detection logic pipeline and its associated tapped pipeline signal combinational logic circuit. The phase detection logic pipeline generates phase detection logic pipeline output signals from a first input clock signal and a second input clock signal. The first input clock signal is applied to a first flip-flop of a set of serially connected flip-flops to generate a pipeline signal. The pipeline signal is driven through the set of serially connected flip-flops by the second clock input signal. Logic pipeline output nodes connected between the serially connected flip-flops carry the phase detection logic pipeline output signals. The phase detection logic pipeline output signals are applied to the tapped pipeline signal combinational logic circuit, which logically combines the signals to generate the phase detection signal.

Abstract: A digital phase detector 100 receives a limited input signal 108 and inputs it and a reference oscillation 112 into an EXCLUSIVE NOR gate 102. The output 110 of the EXCLUSIVE NOR gate 102 is input to a gated N-bit counter 104, which produces an N-bit representation of the magnitude of the phase 115 of the signal 108. A sign detector 105 determines the sign of the phase of the signal by sampling the resultant 110 and combines the magnitude of the phase 115 with the sign of the phase to produce a digital numeric representation of the phase of the signal 116.

Abstract: A circuit is for re-synchronizing an event indication signal received from a foreign domain to generate a result indication signal that is re-synchronized to a host clock signal. The event indication signal is received from the foreign domain at a first input terminal; and a host clock signal is received at a second input terminal. Edge-triggered flip flop circuitry of the circuit has a clock input, a data input, and a data output. The clock input is coupled to the second input terminal and the data input is coupled to receive a latch output signal. The edge-triggered flip flop circuitry clocks the latch output signal to the data output of the flip flop circuitry, to generate a result event indication signal, in response to a transition in the host clock signal. Delay circuitry is coupled to the first input terminal to receive the event indication signal. The delay circuitry provides a delayed event indication signal having a phase that is delayed from the event indication signal.

Abstract: Within a data processing system having two alternative clock signals of different frequencies (fclk, mclk) it is necessary to provide a mechanism for switching between the clock signals. When switching from the fast clock (fclk) to the slow clock (mclk), the system adopts the slow clock from the first falling edge (ffe) after a processing delay (PD) associated with the decision as to whether or not to change clocks. This processing delay can be greater than one half of a cycle of the fast clock. In contrast, when switching from the slow clock to the fast clock, the system adopts the fast clock from the first rising edge (fre) following the processing delay. Thus, a system is provided in which differing strategies for synchronization are adopted depending upon the direction of change of the clock signal.

Abstract: A frequency synthesizer including a phase-locked loop, an oscillator of which supplies n phases with increasing delays of a fast clock signal synchronized on a reference frequency, each of said n phases being sent onto a same number m of fractional dividers having their respective outputs sent onto m jitter compensators which each issue, based on said n phases, a clock signal synchronized on said reference frequency.

Abstract: Described are techniques to stabilize storage devices receiving signals from plural asynchronous docks, especially to avoid "metastability", in particular, a multi-dock pulse synchronizer circuit with an IN-section for receiving and storing prescribed impulses and input cock signals, and for responsively outputting intermediate signals: and an OUT-section for receiving and storing the intermediate pulses, synchronous with certain output clock signals and processing them to generate certain output-signals which avoid metastability.

Abstract: A circuit for generating a low power CPU clock signal is disclosed. The circuit includes a multi-frequency oscillator having a plurality of output signals of various frequencies that are input to a signal selector. The signal selector is controlled to route one of the various frequency signals to the output, which provides the CPU clock oscillating signal. The frequency of the CPU clock signal is compared against a reference oscillatory signal that is generated by a reference oscillator. Based upon the comparison, the frequency comparator generates an output signal that is used to control the signal selector to select an input signal of either higher or lower frequency, depending upon the comparison. Finally, an enable signal is provided for selectively enabling the operation of the CPU clock oscillating circuit.

Abstract: A delay locked loop (44) includes an arbiter circuit (86), a VCD circuit (85), and a collapse detector (88). The arbiter circuit (86) receives an input signal and provides a retard signal to adjust the amount of propagation delay of VCD circuit (85), in order to synchronize the phases of the input signal to an output signal of the VCD circuit (85). The collapse detector (88) detects if the output signal of the VCD circuit (85) has failed to change logic states within a predetermined length of time. The delay locked loop (44) can lock the phases of two signals having different frequencies.

Abstract: An automatic adjustment circuit for an oscillator converts an output from a register into an analog signal by means of a D/A converter. An oscillation frequency of an oscillator is controlled by an output of the D/A converter. A first counter for counting an oscillation signal of the oscillator 1 resets itself and generates a pulse when a count reaches a predetermined value. A second counter counts a reference frequency pulse having a frequency substantially higher than the oscillation frequency of the oscillator. The second counter, on completion of counting a given preset value, changes an output level. The second counter is preset by said first counter when the first counter resets itself. Outputs from the first and the second counters are processed by an AND operation in an AND circuit. A third counter counts an output from the AND circuit, and provides a count output to the register.

Abstract: A synchronizing circuit has a first signal generating unit for dividing a control signal to obtain a first signal having a first frequency, a second signal generating unit for dividing the control signal to obtain a second signal having a second frequency, a third signal generating unit for dividing the control signal to obtain a third signal having a third frequency and synchronized with the second signal, and a synchronizing signal generating unit for generating a synchronizing signal which is adapted to synchronize the first signal with the second and third signals in accordance with a logical operation on the first, second and third signals. With this arrangement, the internal clock signals can be synchronized without using a reset signal. Consequently, neither wiring for supplying the reset signal nor a circuit for generating the reset signal are necessary.

Abstract: A programmable frequency synthesizer includes a first memory (e.g., ROM) for storing a plurality of pre-programmed frequencies, a second memory (e.g., RAM) for storing at least one user input programmable frequency, and dual purpose frequency synthesizer inputs for providing command address information to select one of the pre-programmed frequencies from the first memory and for providing serial data representing a user input programmable frequency to be stored in the second memory. The frequency synthesizer further includes a control input and decoder for directing the address information and the user input programmable frequency data to the first or second memory, respectively.

Abstract: An interface circuit (100) for interfacing an electronic device, such as a microprocessor (102), operating at a device clock speed and a finite synchronous state machine (104) comprised of a D-type flip-flop (106) and a synchronous state machine (108), which are operating at a state clock speed, is provided. The device clock speed being capable of being greater than the state clock speed. The interface circuit.degree. (100) comprises an input circuit, which may comprise a first NAND gate (120), connected to a latch circuit which may comprise interconnected second and third NAND gates (124) and (126). The input circuit and latch circuit store an input signal (121) received from the electronic device and transmit the input signal (121) to the flip-flop (106) when the synchronous state machine (108) is ready to accept further input signals.

Abstract: A method and apparatus for implementing a zero latency synchronizer that permits the reliable transfer of data between clock domains by placing a metastability delay in the clock path. The zero latency synchronizer for synchronizing a signal from a first clock domain to a second clock domain is formed from a clock regenerator circuit and input and output master slave flip flops. The clock regenerator receives a first clock from the first clock domain and a second clock from the second clock domain and generates first and second regenerated clock signals. The first and second regenerated clock signals are formed in a manner that guarantees that the first and second regenerated clocks, in conjunction with the first and second clocks, can be used to control the input and output master slave flip flops and thereby pass data reliably from one clock domain to the other without delay.

Abstract: A data processing system having a first circuit and a second circuit that together control a third circuit by a respective first control signal and a second control signal. The first circuit issues a request signal to the second circuit to trigger initiation of the operation of the third circuit and the second circuit returns a grant signal to the first circuit to indicate that operation of the third circuit has completed. An advance controller within the second circuit serves to start to synchronize the grant signal back to the clock signal of the first circuit at one of a plurality of possible times that is selected to match the relative frequencies of the clock signals driving the first circuit and the second circuit.

Abstract: A digital system including a synchronizer circuit which significantly reduces the occurrence of metastability conditions during data transfer between a first digital subsystem and a second digital subsystem is disclosed. The synchronizer circuit includes a master synchronizer cell and a slave synchronizer cell for handling data transfer from the first subsystem to the second subsystem. Each synchronizer cell includes a signal node, a discharge node, a first discharge patch and a second discharge path, both coupled between the signal node and the discharge node, and a control element coupled to the first discharge path and the second discharge path. The control element selectively activates the first discharge path and the second discharge path in response to an input signal.

Abstract: A multiplexer includes 2.sup.q+1 inputs receiving periodic signals, each signal being out of phase with respect to the other signals, and is controlled so as to switch from a present input signal to a next input signal by activation of a switch signal. The next signal has its phase delayed with respect to the present signal by 360.degree./2.sup.q+1. The switching signal is synchronized with an edge of the next input signal.

Abstract: The present invention provides a data input/output control device integrating a one-chip microcomputer together with a data transfer device and a processor, the data transfer device being constructed to transmit to and receive from an external apparatus serial data and the processor processing data inputted to the data transfer device and transmitting the processed data to the data transfer device to be further transmitted to the external apparatus, the date input/output control device characterized in that a clock of the data input/output control device for an operation thereof is a transfer clock utilized by the external apparatus and the transfer clock is slower than a clock for the processor.

Abstract: If, in a clock generator according to the present invention, the first clock is switched to the second clock with a lower frequency, the frequency count circuit counts the frequency of the second clock with using the first clock as reference. The clock switching control means judges whether the frequency of the second clock is stable or not based on the count result from said frequency count circuit and, if it is stable, switches the switching means for clock switching to the second clock.

Abstract: Data transfer between subsystems of an information handling system employing a multiple subsystem clock environment architecture, or between multiple information handling systems operating with different clock frequencies, is synchronized using a timing aligned multiple frequency synthesizer with a synchronization window decoder. A frequency generation circuit in circuit communication with a data synchronization circuit functions to produce a synchronized timing signal(s) to permit a central processing unit operating in one subsystem clock environment to function with a peripheral subsystem(s), such as a memory controller, operating in a different subsystem clock environment, or permits information handling systems operating with different clock frequencies to function with one another. Data transfer synchronization delays are reduced and mean-time-to-failure of signal synchronization accuracy is increased by eliminating metastability effects from the synchronization circuitry.

Abstract: An apparatus for generating a control signal including pulses occurring at a first frequency f1 and having an overall mean frequency f2 which is in an exact ratio to the difference between the frequencies of a reference signal N and an offset signal O has a common oscillator 18 operating at the frequency of the reference signal N. The offset signal O is produced from the oscillator 18 by a first channel 24a of a 2-channel direct digital synthesizer (DDS), and the frequency f1 is generated by its second channel 24b. The offset signal O controls the rate at which data is entered into a first-in first-out store (FIFO) 54. The signal from the second channel 24b of the DDS triggers sub-sequences of pulses to produce the required control signal, which modifies the extraction of data from the FIFO 54 occurring at the rate of the reference signal N. Each sub-sequence may include one pulse, no pulse or two pulses.

Abstract: Adaptive clock generator including a master clock. A control means detects the current operating mode and, in response, provides a corresponding integer output N. A programmable pulse generator provides an output clock signal comprising a "high" pulse having a predetermined width followed by a "low" pulse having a width of N master clock periods. A dithered clock signal may be provided when the control means provides an integer output N selected from a set of integer values. Preferably, N is selected in a random or pseudo-random manner.

Abstract: A digital clock circuit generates a high-speed clock and window pulses substantially centered about transitions of the high-speed clock in one quadrant of an integrated circuit (IC) and routes the high-speed clock and window pulses to other quadrants of the IC where a low-speed clock generator develops a low-speed clock signal from the window pulses. A control circuit checks alignment between the high-speed and low-speed clock signals and adjusts first and second shift registers to control the delay in generating the low-speed clock as necessary to maintain alignment. The first shift register controls the falling edge of the low-speed clock signal and the second shift register controls the rising edge of the low-speed clock signal.