Abstract: The invention relates to a method for synchronizing a first clock C to a reference clock A, the first clock C being connected to said reference clock A via a processing unit B. The invention moreover relates to a processing unit B and to a synchronization system. In order to enable a synchronization of said first clock C to said reference clock A via said processing, unti B. it is proposed that the processing unit B generates a correction message cmsg for the first clock C based on timestamps exchanged between the processing unit B and the reference clock A, which exchanged of timestamps is triggered by clock pulses cclk received in the processing unit B from the first clock C.

Abstract: A method and apparatus for emulating a high-precision, high-accuracy clock. In one embodiment, two clocks are used in the emulation. The first clock has precision greater than precision of the second clock and accuracy less than accuracy of the second clock. A checkpoint time relative to elapsed cycles of the second clock and a checkpoint cycle count of cycles of the first clock are periodically stored relative to a checkpoint period that lasts for a selected number of cycles of the second clock. A reference cycle rate of the first clock is calculated relative to the cycle rate of the second clock. The current time is determined as a function of the checkpoint time, a number of cycles of the first clock elapsed since storing the most recent checkpoint cycle count, and the reference cycle rate of the first clock.

Abstract: A method for processing data is provided that includes receiving a clock signal at a source driver and communicating the clock signal to a plurality of destination receivers. The clock signal may be received at the destination receivers during a substantially equivalent time interval, the plurality of destination receivers being five.

Abstract: A clock may be generated having a predetermined unit interval. Received data may then be compared to the virtual clock to determine whether more than one data change occurs during a particular unit interval. If more than one data change occurs during a particular unit interval, the virtual clock may not correspond to the source clock. The virtual clock may then be incremented by a phase shift offset and the data analyzed again. When a phase shift virtual clock is identified that aligns with the data such that a plurality of data changes do not occur during a given unit interval, the embodiment may determine that a passing virtual clock may have been identified.

Abstract: An interface circuit according to one embodiment of the present invention includes a clock signal, a first phase locked loop coupled to the clock signal line and generating a reference clock signal, a second phase locked loop receiving the reference clock signal, and in accordance therewith, generating one or more phase shifted reference clock signals, and a data transceiver circuit coupled to receive at least one of the clock signal, the reference clock signal, or one or more of the phase shifted reference clock signals to control the flow of data between a first circuit and a second circuit. An interface circuit according to one embodiment of the invention can be used advantageously for controlling the flow of data between a CPU and an external memory.

Abstract: An adjustable logic circuit includes a pulse filter and delay circuit, a state machine and combinational logic circuit, and a data strobe generation circuit. The pulse filter and delay circuit is operative to read an adjustable configuration value and, based thereon, to implement a delay between an internal clock and both a data signal and a data strobe signal, the delay being a fraction of a clock period. The state machine and combinational logic circuit are operative to select a data value from a plurality of data values, and to provide a data signal based upon the data value. The data strobe generation circuit is operative to provide the data strobe signal at a time when both the data signal is valid and the delay is compatible with a predetermined external device.

Abstract: Data is communicated through two separate circuits or circuit groups, each having clock and mode inputs, by sequentially reversing the role of the clock and mode inputs. The data communication circuits have data inputs, data outputs, a clock input for timing or synchronizing the data input and/or output communication, and a mode input for controlling the data input and/or output communication. A clock/mode signal connects to the clock input of one circuit and to the mode input of the other circuit. A mode/clock signal connects to the mode input of the one circuit and to the clock input of the other circuit. The role of the mode and clock signals on the mode/clock and clock/mode signals, or their reversal, selects one or the other of the data communication circuits.

Abstract: A method and apparatus are disclosed for dynamically reducing clock skew among various nodes on an integrated circuit. The disclosed clock skew reduction technique dynamically estimates the clock delay to each node and inserts a corresponding delay for each node such that the clock signals arriving at each node are all in phase with a global clock (or 180° out of phase). Delays attributable to both the wire RC delays and the clock buffer delays are addressed. A feedback path for the clock signal associated with each node allows the round trip travel time of the clock signal to be estimated. When the length of the feedback path matches the length of the primary clock path, the clock skew present at the corresponding node can be estimated as fifty percent (50%) of the round trip delay time. Dynamic adjustments to the delay control circuit are permitted as operating conditions shift.

Abstract: A sampling device includes a first delay circuit and a second delay circuit in a parallel configuration, where the first delay circuit and the second delay circuit are responsive to a clock signal. A data sampling circuit may use an output of the first delay circuit and an output of the second delay circuit to sample a data signal synchronized with the clock signal. The data signal and the clock signal may be synchronized according to a double data rate (DDR) protocol.

Abstract: An interfacing logic is implemented in one or more processors and a memory controller in a multiprocessor system. The interfacing logic enables all processors to receive snoops and snoop responses substantially at the same time by delaying data transmitted over faster busses before the data is provided to a local logic at a receiving end of the faster busses. The interfacing logic comprises two or more paths of a multiplexer component connected to a storage component. The storage components are connected to another multiplexer component for selecting one of the two or more paths. Preferably, a bus control logic in the receiving end determines how much delay is performed to compensate for delay differences between data busses.

Abstract: A rate limiting circuit for data stream transmissions provides a generated clock signal to a buffer interposed between source and destination components so as to programmably adjust the maximum rate that data can be passed through the buffer. A counter is incremented by one each (1+RLmax) cycles of a clock signal, where RLmax is the larger of a user programmable value (RL) and a manufacturer one-time programmed value (SERL). A controller receiving a request to access the buffer for a read or write operation, checks the count of the counter before activating the access enable line. If the count is greater than zero, then the controller activates the access enable line while decrementing the counter by one. If the count is zero, however, then the controller waits until the count is greater than zero before activating the access enable line to grant the request.

Abstract: A method for selectively deskewing data traveling through a bus in a network device is disclosed. Bit-level data is received from each data line of a plurality of data lines of the bus. Vertical line information is detected for the plurality of data lines to determine if there is a match with a training pattern. A skew distance is calculated once there is a match with the training pattern. Then, the plurality of data lines are bit aligned based on the skew distance.

Abstract: A technique includes receiving a first signal from a data signal line. The first signal includes an edge that is indicative of a transition between logical states. The first signal is sampled at different times to form a plurality of sampled signals. In response to the sampled signals, the technique includes selecting a subset of the times to sample data from the data signal line.

Abstract: A method and circuit adaptively adjust respective timing offsets of digital signals relative to a clock output along with the digital signals to enable a latch receiving the digital signals to store the signals responsive to the clock. A phase command for each digital signal is stored in an associated storage circuit and defines a timing offset between the corresponding digital signal and the clock. The clock is output along with each digital signal having the timing offset defined by the corresponding phase command and the digital signals are captured responsive to the clock and evaluated to determine if each digital signal was successfully captured. A phase adjustment command adjusts the value of each phase command. These operations are repeated for a plurality of phase adjustment commands until respective final phase commands allowing all digital signals to be successfully captured is determined and stored in the storage circuits.

Abstract: A communication channel includes a first component having a transmitter coupled to a normal signal source, and a second component having a receiver coupled to a normal signal destination. A communication link couples the first and second components. Calibration logic provides for setting an operation value for a parameter of the communication channel, such as by executing an exhaustive calibration sequence at initialization of the link. A tracking circuit, including a monitoring function, tracks drift in the parameter by monitoring a feedback signal that has a characteristic that correlates with drift in the communication channel, and updates, or indicates the need for updating of, the operation value of the parameter in response to the monitoring function.

Abstract: Improved techniques are provided for detecting and correcting errors and skew in inter-cluster communications within computer systems having a plurality of multi-processor clusters. The local nodes of each cluster include a plurality of processors and an interconnection controller. Intra-cluster links are formed between the local nodes, including the interconnection controller, within a cluster. Inter-cluster links are formed between interconnection controllers of different clusters. Intra-cluster packets may be serialized and encapsulated as inter-cluster packets for transmission on inter-cluster links, preferably with link-layer encapsulation. Each inter-cluster packet may include a sequence identifier and error information computed for that packet. Clock data may be embedded in symbols sent on each bit lane of the inter-cluster links. Copies of transmitted inter-cluster packets may be stored until an acknowledgement is received.

Abstract: A memory system of a high-speed operation can be realized by reducing an influence of reflection signals etc. caused by branching and impedance mismatching in various wirings between a memory controller and a memory module, and an influence due to transmission delays of data, command/address, and clocks in the memory module. To this end, a memory system comprises a memory controller and a memory module mounted with DRAMs. A buffer is mounted on the memory module. The buffer and the memory controller are connected to each other via data wiring, command/address wiring, and clock wiring. The DRAMs and the buffer on the memory module are connected to each other via internal data wiring, internal command/address wiring, and internal cock wiring. The data wiring, the command/address wiring, and the clock wiring may be connected to buffers of other memory modules in cascade.

Abstract: A method for transferring variable isochronous data and an apparatus therefor are provided. The method for transferring variable isochronous data includes the steps of (a) determining isochronous transfer to be terminated when the bus is in an idle state for a time interval which is larger than an isochronous gap period, (b) detecting a residual gap having a time interval which is larger than the time interval of an isochronous gap and smaller than the time interval of a subaction gap, (c) checking whether bandwidth for the transfer of isochronous data remains when the residual gap is detected in the step (b), and (d) transferring the isochronous data when it is determined that the bandwidth remains in the step (c).

Abstract: Clock data recovery (CDR) circuitry or phase locked loop (PLL) circuitry can be provided with a dynamically adjustable bandwidth. One CDR circuit or PLL circuit can be provided to support multiple systems or protocols, multiple parameter requirements for a given system or protocol, and changes in the input frequency or data rate within a given system or protocol. The parameters can include jitter (e.g., jitter tolerance, jitter transfer, jitter generation), source of dominant noise, and lock time. Control signals can be used to dynamically adjust the bandwidth of the CDR circuitry or PLL circuitry while the circuitry is processing data. The control signals can be set by a PLD, by a processor, by circuitry external to the PLD, or by user input.

Abstract: A low-pass filter in a read channel, having an adjustable cutoff frequency has a low-pass filter 14, a time measuring circuit 15, a storage computing circuit 19 and a current supply circuit 18. The time measuring circuit 15 computes the pulse number of a reference clocking signal. The storage computing circuit 19 obtains the mean value of first and second set values that correspond to current values of the control current when the pulse number of the reference clocking signal increases by 1, and the current supply circuit 18 supplies a control current equivalent to the mean value to the low-pass filter 14. Therefore, even if the same pulse number is computed more than once, the desired current set value can be obtained from the mean value of the first and the second set values, and a control current amount that corresponds to said current set value can be supplied.

Abstract: The present invention comprises a memory device for compensating for a clock skew that generates a centering error, and a method of compensating for the clock skew. To compensate for a clock skew that causes a centering error between an external clock signal and an output data signal, the memory device includes a phase detector (PD) and an up-down counter. The PD detects a phase difference between the output data signal and the external clock signal and generates an up signal or a down signal depending on the detected phase difference. The up-down counter is enabled by a calibration signal that directs a compensation of the skew and generates an offset code in response to the up signal or the down signal. The offset code is fed back to a delay locked loop (DLL) circuit and aligns the middle points of the output data signal with the edges of the external clock signal.

Abstract: An apparatus for enhancing the speed of a synchronous bus includes a two register based FIFO with software control bits and a second clock signal. According to the invention, the second clock signal rd_clk is supplied by the same PLL that provides the main clock signal lg_clk. According to the invention, data is taken from the two registers in alternative clock cycles so that each of the register holds valid data for two clock cycles. A first software data bit is used to determine which of the two registers is unloaded first. Using the method and structure of the invention, the window for transferring valid data is increased and therefore the system employing the method and apparatus of the invention is more skew tolerant.

Abstract: A master clock reference signal may be provided to selected packet fiber nodes in order to synchronize the local clock reference signals generated at selected devices in a cable network. In this way, selected portions of the cable network may be synchronized to a common timing reference signal. Additionally, synchronized timestamp information may also be provided to selected network devices in order to achieve synchronization of timestamps across a selected portion of the cable network.

Abstract: A ring oscillator has a first logic circuit forming a first loop. The ring oscillator also has a second logic circuit forming a second loop, such that phase interpolation occurs at a node common to the first and second loops. The phase interpolation results in an output signal with a high frequency.

Abstract: There is disclosed a sample selection and data alignment circuit that is able to recover (retime) a data on a predefined phase of a multiphase clock signal. A plurality of over sampled signals (G0, . . . , Gn?1) is obtained by over sampling an incoming serial binary data (bits) stream with the n phases (G0, . . . , Gn?1) of a multiphase clock signal. A reliable over sampled signal is selected according to a selected signal (G0, . . . , Gn?1) generated by an edge detector which designates which over sampled signal is the best for subsequent processing.

Abstract: A clock-synchronizing apparatus and method of devices with different clocks are disclosed. Between a first device operated with a first clock and a second device operated with a second clock faster than the first clock, an operation latency of the second device refers to the first clock, control signals that controls the second device are generated at the second clock speed according to the operation latency, and an enable interval of the control signals has a 1/4 clock period of the first clock. Accordingly, since the first device and the second device can transmit and receive a data to and from each other while being operated by using their own clock, an access latency for the first device to access the second device can be reduced and a transmission band width between the two devices can be effectively used.

Abstract: In a system and method for managing the operating frequency of processors in a blade-based computer system, a circuit receives a signal with instructions relating to the desired operating frequency of the processors or blades. The circuit then generates a control signal based upon the specific frequency designated by the user. A frequency synthesizer then processes an input frequency signal and the control signal and outputs an output frequency to be used by at least one processor in the blade-based computer system.

Abstract: In one form of the invention, a method for generating a local clock signal responsive to signals on a Universal Serial Bus (“USB”) includes generating a frequency-bearing clock signal by a free running oscillator on an integrated circuitry chip of a device coupled to the USB. The oscillator runs at a frequency that is substantially stable but initially known with substantial inaccuracy. A single ended bit-serial signal is extracted from received signals sent by a USB host or hub and timing signals are responsively asserted. A bit pattern is detected in the single ended bit-serial signal and intervals are measured during which the timing signals are asserted. The period P of the local clock signal is adjusted responsive to one of the measured intervals. In one variant, the initial inaccuracy is at least partly because the oscillator consists solely of circuitry on the chip.

Abstract: A system and method for aligning an input signal (24) synchronized to a first clock signal (22) with a second clock signal (26). The invention includes a mechanism (106) for generating a third clock signal (354) and an arrangement (352) for loading the input signal (24) in accordance with the third clock signal (354) and reading out an output signal in accordance with the second clock signal (26). In an illustrative embodiment, the invention is used in a sensor system (350) to align detector input data (24), which is synchronized to a data-capture clock (22), with a signal-processing clock (26). The register (352) acts as a data path transitioning stage between the actual time the input data is sampled and the time a processing system (102) clocks in the sampled data.

Abstract: A closed-loop based timing signal distribution architecture includes at least one signal source coupled to a signal path disposed in a closed loop arrangement to facilitate generation of a standing wave signal within the signal path. In one embodiment, at least one receiver is coupled to the signal path to generate at least one digital clock signal based upon the standing wave signal.

Abstract: Disclosed is a method and circuit for variably controlling a delay line for a read data capture timing window. In one embodiment, the circuit includes a variably controlled delay circuit coupled to a FIFO. The variably controlled delay circuit receives an input strobe signal. The variably controlled delay circuit also receives a multibit control code. The variably controlled delay circuit transmits the input strobe signal after a time delay, wherein the time delay varies according to the multibit control code. The FIFO is coupled to the variably controlled delay circuit and receives the time delayed strobe signal therefrom. The FIFO receives an input data bit signal. The FIFO stores the input data bit signal in response to receiving the time delayed strobe signal.

Abstract: A phase difference delay control system is provided that enables distance measurement between a reference position and a terminal at the time of recovery after a line has been disconnected as a result of fluctuation of phase difference of clock crossover units.

Abstract: Method and apparatus for reducing effect of jitter is described. More particularly, one or more taps of a delay line are selected for a reference clock signal. These selected taps each have an associated index, which is stored, and stored indices are statistically processed to select a tap of another delay line.

Abstract: A method for determining a read strobe pulse delay for data read from a memory having a plurality of memory chips. Each one of the chips provides data along with an associated read strobe pulse. The data read from each one of the plurality of chips is stored in a corresponding one of a plurality of storage devices in response to the read strobe pulse associated with such one of the plurality of chips. A training system determines a delay which when applied in to the plurality of read strobe pulses enables valid read data from the plurality of memory chips to be stored in each one of the plurality of the storage device in response to the read strobe pulses being delayed by the read pulse strobe delay. A process is used to enable preservation of the user data during the training process for use subsequent to the training process.

Abstract: A programmable logic device has programmable phase-shifting circuitry. The phase-shifting circuitry is used to generate a set of skewed clock signals that is used to adjust the relative timing of device elements in a circuit synthesized in the programmable logic device. By suitably adjusting the relative timing of the device elements, the circuit critical path lengths are effectively reduced leading to improved circuit frequency performance. Algorithms are provided for establishing clock skew values that lead to improved circuit performance. The algorithms are incorporated in computer aided design tools to enable automatic optimization of circuit designs.

Abstract: A system includes modules, a clock generator that generates a first clock signal that is applied to the modules, and a chipset that controls the modules, the chipset having a clock buffer that generates a second clock signal. The system includes a first clock line that transfer the first clock signal to the clock buffer, the first clock line connected between the clock generator and a first termination circuit. The system includes a second clock line that transfer the second clock signal to the modules, the second clock line electrically isolated from the first clock line, the second clock line connected between the clock buffer and a second termination circuit.

Abstract: An interleaved delay line for use in phase locked and delay locked loops is comprised of a first portion providing a variable amount of delay substantially independently of process, temperature and voltage (PVT) variations while a second portion, in series with the first portion, provides a variable amount of delay that substantially tracks changes in process, temperature, and voltage variations. By combining, or interleaving, the two types of delay, single and dual locked loops constructed using the present invention achieve a desired jitter performance under PVT variations, dynamically track the delay variations of one coarse tap without a large number of delay taps, and provide for quick and tight locking. Methods of operating delay lines and locked loops are also disclosed.

Abstract: Disclosed is a clock distribution device and method in a compact PCI system based multi-processing system. A compact PCI based multi-processing system preferably includes processing signals upon mounting various circuit boards on multiple slots, even if the location of the system slot is varied, the skew of clocks transmitted to the other slots may be minimized. Accordingly, the system may be configured in a flexible manner because of such variability of the system slot's location. Further, the system may be efficiently repaired and maintained because it is possible to easily and quickly take measures in response to any failure occurring on the board mounted on the system slot.

Abstract: A data transmission error reduction circuit is formed including a delay circuit, a detection circuit and a control circuit. In one embodiment, the delay circuit includes n delay element and multiplexor pairs, selectively employable to apply an aggregate amount of time delay to a data signal. The detection circuit includes circuit elements to detect a critical reference time distance between a reference point of a data signal and at least a selected edge of a clock signal being smaller than a desired threshold. The control circuit includes circuit elements to dynamically control the aggregate amount of time delay applied by the delay circuit based at least in part on the detection of the detection circuit. In one application, m units of the data transmission error reduction circuit are correspondingly employed to reduce data transmission errors on m high speed parallel data signals of a data interface.

Abstract: A high-speed digital interface circuit for use with an N bit digital data signal is disclosed. The circuit comprises a source device that initially receives the N bit digital data signal, and a sink device that receives the N bit digital data signal from the source device. The N bit digital data signal has a skew when received by the sink device. A skew detection circuit in the sink device detects the skew in the N bit digital data signal and generates a skew detection signal. A line supplies the skew detection signal to the source device. A compensation circuit in the source device receives the skew detection signal and compensates for the skew in the N bit digital data signal.

Abstract: The invention provides for the arrangement and management of timing of various domains on a large integrated circuit which introduces a phase offset between clock domains of neighboring cells to create a wavefront clock which propagates through the circuit at the same speed data propagates though the circuit. The cells of the integrated circuit are wavefront clock synchronized in that the phase offset introduced in a particular cell's clock is such that the arrival of a skewed clock and propagation delayed data from that cell's neighbor is synchronized with that particular cell's own clock. Wavefront clock synchronization mitigates at least some of the problems of clock skew and the associated effects of slowing data propagation and reduction of clock frequencies associated with large surface integrated circuits utilizing synchronized clock domains.

Abstract: A local timer includes a dividing counter which counts a first clock and outputs a reference counting signal divided from the first clock; a timing synchronizing timer which counts a timing synchronizing timer value in synchronization with a reference timer responsive to the reference counting signal; a first buffer which stores a counted value of the dividing counter in synchronization with a second clock, when operation is by the first clock; a second buffer which stores the timing synchronizing timer value in synchronization with the second clock, when operation is by the first clock; a first adder which adds a first or second offset value to the stored value in the first buffer in synchronization with the second clock, when the first clock is suspended; and a second adder which adds a set value to the timing synchronizing timer value responsive to a carry from the first adder.

Abstract: A data processing system includes first, second, and third agents connected to a shared bus. The third agent is able to receive information via the shared bus from the first agent or from the second agent. The third agent includes a skew compensation circuit to determine signal skew in signal received via the shared bus and to compensate for the skew by adding delay into selected signals of the bus. The skew compensation circuit determines whether the first agent or the second agent is the sender of information received by the third agent via the shared bus. The skew compensation circuit alters the skew compensation based on the identity of the sender such that the delay into the bus signals is specific to the corresponding sender.

Abstract: Clock and data recovery circuitry is provided that is used in integrated circuits such as programmable logic device integrated circuits. The clock and data recovery circuitry may recover digital data and an embedded clock from a high-speed differential input data stream. The clock and data recovery circuitry may have automatic mode switching capabilities. When operated in reference mode, the clock and data recovery circuit may use a first phase-locked loop to lock onto a reference clock. When operated in data mode, the clock and data recovery circuit may use a second phase-locked loop to lock onto the phase of the differential data stream. A control circuit may automatically switch the clock and data recovery circuit between the reference mode and the data mode. Override signals may be used to force the clock and data recovery circuit out of the automatic mode and into either the reference or data mode.

Abstract: A method for generating a signal pulse sequence with a predetermined stable fundamental frequency from a sequence of signal pulses whose frequency fluctuates and has the spectral components whose frequency is at least a predetermined multiple of the fundamental frequency. The method includes, feeding the sequence of signal pulses to a digital filter, arranging a passband of the digital filter around the fundamental frequency, blocking, using the digital filter, around a predetermined half the sampling frequency. The method further includes outputting a signed output signal when the digital filter is excited, and generating a clock signal pulse for each change in sign of the output signal.

Abstract: A high-speed parallel data communication approach overcomes data skewing concerns by concurrently transmitting data in a plurality of multiple-bit groups and, after receiving the concurrently-transmitted data, realigning skew-caused misalignments between the groups. In one particular example embodiment, for each group, an arrangement transfers the data in parallel and along with a clock signal for synchronizing digital data. The transferred digital data is synchronously collected via the clock signal for the group. At the receiving module, the data collected for each group is aligned using each group's dedicated clock signal. Skew across clock-domain groups is tolerated and overcome by processing the data and the skew first within each clock domain group, and then between groups.

Abstract: A method for controlled synchronization to an astable clock system, and reception unit corresponding thereto are disclosed. Soft synchronization using a slight change in the period duration of the clock signal produced makes it possible to alter said clock signal such that a phase difference between the stable clock signal produced by a phased locked loop upon a synchronization signal and the clock signal produced for an application is slowly reduced until the two clock signals are in synchronization with one another after a period of time.

Abstract: One embodiment of the present invention provides a system that provides skew compensation for communications across a source-synchronous self-timed network. During each clock period, the system allows multiple synchronous transmitters to each transmit one data element and to assert one acknowledgement on a transmit clock line into the self-timed network. In doing so, the multiple synchronous transmitters do not wait for requests from the self-timed network before transmitting a subsequent data element. Similarly, during each clock period, the system allows multiple synchronous receivers to accept one data element from and to assert one request on a receive clock line coupled into the self-timed network. In doing so, the multiple synchronous receivers do not wait for acknowledgments from the self-timed network before receiving a subsequent data element. The self-timed network is configured to tolerate bounded skew between the multiple synchronous transmitters and multiple synchronous receivers.

Abstract: A memory system and method according to various aspects of the present invention comprises a memory and an adaptive timing system for controlling access to the memory. The adaptive timing system captures data in a data valid window (DVW) in a data signal. In one embodiment, the adaptive timing system comprises a delay circuit for sampling the data signal at a midpoint of the DVW. The adaptive timing system may also comprise an identifying circuit for identifying whether the midpoint of the DVW corresponds to an actual midpoint of the DVW and adjusting the delay circuit accordingly.

Abstract: To provide a semiconductor circuit device including a synchronous frequency divider which counts input clock signals and outputs a counted value, a selector circuit which receives signals of bits of the counted value output from the synchronous frequency divider and outputs a carry look-ahead signal of predetermined bits as an operation-processing effective-state signal in accordance with a selector signal, and an integrated circuit portion which uses a clock signal input to the synchronous frequency divider as a source clock and whose operating frequency is switched in accordance with the operation-processing effective-state signal.