JPH06250755A - Electronic equipment - Google Patents

Abstract

PURPOSE:To suppress an unnecessary electromagnetic field which is radiated and enable strict time control by imposing frequency modulation on a system clock and processing data on the basis of information from a timer circuit including a stable oscillator. CONSTITUTION:A voltage-controlled oscillator 6 varies the oscillation frequency of a signal from a low frequency oscillator 5 and sends its output to respective control circuits as the system clock 16 while dividing frequency into (n) (n is integer) by a frequency divider 7 and varying the frequency division output at a repetitive period within a specific range. When a program is executed, a crystal oscillator 9 oscillates at a stable frequency and its output is supplied to a timer controller 8. The timer controller 8 counts the output signal of the crystal oscillator 9 and outputs an interruption request to a microprocessor 1 when the counted value reaches a specific value. The processor 1 executes the specific program in synchronism with the interruption request. At this time, the influence of electromagnetic radiation on the control circuits is reduced because of the frequency modulation imposed on the system clock 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device which suppresses emission of unnecessary electromagnetic waves by modulating a system clock.

[0002]

2. Description of the Related Art In recent years, the processing speed of microprocessors has dramatically improved, and the processing capacity of personal computers, workstations, page printers, etc. using this high-speed microprocessor has also dramatically improved. . Then, as the processing speed is improved, unnecessary electromagnetic radiation from the microprocessor and its peripheral circuits is also increased, so-called EMI (Electro-Magne).
tic Interference) measures have become difficult.

The main reasons for the increase of the unnecessary electromagnetic radiation are as follows. 1) The operating clock frequency of the device is high. For example, in a microprocessor manufactured by a CMOS process, the operating clock frequency is 25 MHz, 33M
It is becoming high frequency like Hz. When the clock frequency becomes high, the harmonic components in the high frequency band included in the clock signal become large, and the electromagnetic field at the high frequency is easily radiated from the small equivalent antenna. It is also easily radiated from the signal line.

2) The circuit scale of the device is increasing. Currently, microprocessors are available from 16 bit processing type to 3
With the shift to the 2-bit processing type, the number of signal lines on the circuit board also increases, and unnecessary electromagnetic radiation increases.
Also, the number of gates inside the microprocessor increases,
For example, microprocessors with hundreds of thousands of gates have also appeared.

Further, the number of gates in the peripheral circuit of the microprocessor is increased, so that the electromagnetic field leaking from the signal line and the power supply line is also increased. As measures against the above-mentioned EMI, conventionally, several methods have been used, for example, strengthening an electromagnetic shield or providing a filter on a signal line or a power supply line. Also, a method of frequency modulating a reference clock has been devised.

Therefore, a method of frequency-modulating the reference clock will be briefly described. The microprocessor generally operates in synchronization with a square wave system clock having a constant period. Therefore, the harmonic frequency spectrum emitted from the system clock line or the system bus of the microprocessor becomes a discrete spectrum arranged at constant frequency intervals as shown in FIG.

On the other hand, when modulated with the frequency of this square wave system clock, its harmonic frequency spectrum becomes
So-called sidebands occur at frequencies around each harmonic shown in FIG. 2 (FIG. 3). Then, the level of the peak value of each harmonic spectrum of the frequency generated when the frequency modulation is not performed is lowered by this modulation. Therefore, the unnecessary radiation electromagnetic field of a specific frequency is lowered, which is effective as EMI. On the other hand, depending on whether the frequency of the system clock is modulated or not,
There is almost no change in the total power radiated in all frequency bands.

As described above, the peak value of the high frequency frequency spectrum emitted from the square wave clock is lower than that obtained by frequency-modulating the square wave. At this time, if the instantaneous frequency deviation of the modulated signal is large, the peak value is large. As the band width of the sideband becomes wider, the peak value of the spectrum becomes lower.
Therefore, in order to improve the effect of the EMI countermeasure, it is necessary to increase the instantaneous frequency deviation of the system clock.
For example, for a microprocessor operating at a maximum system clock of 25 MHz, a sufficient effect can be obtained by shifting the system clock from 24 MHz to 25 MHz.

[0009]

However, in the above-mentioned conventional EMI countermeasures, the instantaneous frequency deviation of the system clock must be increased in order to obtain a sufficient effect thereby, so that the center frequency of the system clock is reduced. There is a problem that it becomes difficult to stabilize. For example,
Voltage controlled crystal oscillator (generally abbreviated as VCXO)
, The center frequency is stable, but the frequency deviation cannot be increased. Further, if the crystal oscillator is not used, the center frequency cannot be stabilized even if the frequency deviation can be made large, which causes a problem that the microprocessor cannot perform strict time control for time management. is there.

An object of the present invention is to provide an electronic device capable of suppressing unnecessary electromagnetic fields emitted from a microprocessor and its peripheral circuits and performing strict time management.

[0011]

To achieve the above object, the present invention comprises a microprocessor and a plurality of control units which are controlled by the microprocessor, and the microprocessor and the control unit are of a bus type. In an electronic device which operates by receiving the supply of a predetermined clock pulse via the signal line, means for frequency-modulating a high-frequency signal with a low-frequency signal and 1 / n frequency division (n) of the frequency-modulated signal. Is an integer) to generate the clock pulse, an oscillating means for generating a signal having a constant cycle, a means for counting the signal having the constant cycle, and an interrupt to the microprocessor based on the counting result. Generating means, and the microprocessor operates in synchronization with the interrupt.

[0012]

In the above structure, the unnecessary electromagnetic field emitted is suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. [First Embodiment] FIG. 1 is a block diagram showing the arrangement of a personal computer according to the first embodiment of the present invention.
In the figure, reference numeral 1 is a microprocessor, 2 is a memory controller, 8 is a timer controller, and 10 is C.
An RT controller, 12 is an input / output port, and 14 is a hard disk controller, all of which are connected to the system bus 4 and a system clock 16 is supplied.

Here, the system bus 4 includes an address bus, a data bus, a controller bus, an interrupt request signal, etc. of the microprocessor 1. Reference numeral 5 is, for example, a low frequency oscillator having a frequency of about 100 KHz.
Further, 6 is a voltage controlled oscillator (hereinafter abbreviated as VCO)
The oscillation frequency changes according to the signal received from the low frequency oscillator 5. For example, when the center frequency of the VCO 6 is 49 MHz and the instantaneous frequency deviation is ± 1 MHz, the instantaneous frequency of the output of the VCO 6 is 48 MHz to 5 MHz.
It changes in a cycle of 100 kHz up to 0 MHz.

The output of the VCO 6 is frequency-divided by the 1/2 frequency divider 7, the output of which is a rectangular pulse, and the repetition period of the pulse changes from 24 MHz to 25 MHz. The output of the 1/2 frequency divider 7 is used as the system clock as described above, including the microprocessor 1, the memory controller 2, the timer controller 8, the CRT controller 10, the input / output port 12, and the hard disk controller. -It is input to LA14.

The microprocessor 1 accesses the memory controller 2, the timer controller 8, the CRT controller 10, the input / output port 12, and the hard disk controller 14 in synchronization with the above system clock. For example, the microprocessor 1 fetches the program stored in the semiconductor memory 3 via the memory controller 2. Then, the microprocessor 1 executes the program and stores the execution result in the semiconductor memory 3 via the memory controller 2 as well.

The memory controller 2 controls the timing of memory access. If the semiconductor memory 3 includes a dynamic random access memory (DRAM), the memory controller 2 also refreshes the DRAM. . Also, the microprocessor 1
Receives the key input data sent from the keyboard 13 via the input / output port 12. Then, the microprocessor 1 interprets the received key input data according to the program stored in the semiconductor memory 3 and executes the command of the key input data. Then, the microprocessor 1 stores the execution result for the key input data in the semiconductor memory 3 or sends the execution result to the CRT controller 10.

The CRT controller 10 receives the data received from the microprocessor 1 from blue (B), green (G),
The data is converted into red (R) three-color raster data and sent to the CRT display 11. As a result, the personal computer can display the result executed by the microprocessor 1. Furthermore, the microprocessor 1
Accesses the hard disk drive 15, which is an external storage device, via the hard disk controller 14. The microprocessor 1 reads the program stored in the hard disk drive 15 and stores the program in the semiconductor memory 3. Then, the program stored in the semiconductor memory 3 is executed, and the executed result is stored again in the semiconductor memory 3, displayed on the CRT display 11, or stored again in the hard disk drive 15, for example.

The program described above is executed based on the output of the timer controller 8. Also,
The crystal oscillator 9 is an oscillator that oscillates at a stable frequency, and its output is input to the timer controller 8.
The timer controller 8 counts the output signal of the crystal oscillator 9, and the microprocessor 1 sets the system bus 4
Read the count value via. When the count value reaches a predetermined value, the timer controller 8 outputs an interrupt request to the microprocessor 1 via the system bus.

The microprocessor 1 executes a predetermined program in synchronism with the above-mentioned interrupt request, and the memory controller 2, the timer controller 8, the CRT controller 10, the input / output port 12, the hard disk controller. 14 is controlled. The system clock 16 includes a memory controller 2, a timer controller 8 and a CRT.
Since the signal is supplied to the controller 10, the input / output port 12, and the hard disk controller 14, the signal line length of the clock line becomes long. Also, the scale of the connected circuit is large. Therefore, the harmonic components of the system clock are likely to be emitted to the outside.

However, here, since the system clock 16 is frequency-modulated, the peak value of the spectrum at a specific frequency is small, and as a result, the influence of EMI is small. On the other hand, crystal oscillator 9
Is connected only to the timer controller 8, so that the clock line of the crystal oscillator 9 can be shortened. Furthermore, the oscillation frequency of the crystal oscillator 9 is several MH.
Since it can be made as low as z, harmonics are less likely to be emitted from the peripheral circuit of the crystal oscillator 9, and the peak value thereof is also low.

Since the crystal oscillator 9 is a stable oscillation source, the microprocessor 1 can perform strict time control. As described above, according to the present embodiment, the system clock for the microprocessor is frequency-modulated, and the system bus of the microprocessor is provided with the timer circuit including the oscillator for stable oscillation. By performing the data processing based on the information received from the circuit, stable time management of the device can be executed, and the influence of the EMI due to the system clock can be reduced. [Second Embodiment] FIG. 4 is a block diagram showing the arrangement of a laser beam printer according to the second embodiment of the present invention.

In FIG. 4, the same components as those of the personal computer according to the first embodiment shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted here. In the laser beam printer shown in FIG. 4, the external computer device 24 sends coded image data to the input / output port 22 via the external interface 23. Then, the microprocessor 1 is connected to the system bus 4
After receiving the coded image data from the input / output port 22 via the, the coded data is converted into bitmap raster data, and the raster data is transferred to the semiconductor memory via the memory controller 2. Store in 3.

When the microprocessor 1 completes the conversion of one page of raster data, the microprocessor 1
Causes the DMA controller 17 to become active. The DMA controller 17 accesses the memory controller 2 via the system bus 4 and reads the raster data stored in the semiconductor memory 3 from a predetermined address. Then, the read data is processed by the parallel-serial converter 1 in response to a request from the parallel-serial converter 18.
Send to 8. It should be noted that the microprocessor 1 and the DMA controller 17 monopolize the system bus 4 alternately by time division.

The microprocessor 1 also controls the printer engine 19 via the input / output port 21. Then, when the printer engine 19 is ready for printing, the printer engine 19 sends a horizontal synchronization signal HSYNC to the parallel-serial converter 18. The parallel-to-serial converter 18 synchronizes with D
The raster data received from the MA controller 17 is converted into a serial signal, and the signal is sent to the printer engine 19 as a VIDEO signal.

V output from the parallel-serial converter 18
The reference clock of the IDEO signal is supplied from the crystal oscillator 9. Similarly, the clock output from the crystal oscillator 9 is input to the timer controller 8, and the timer controller 8 counts the clock received from the crystal oscillator 9. Then, the timer controller 8 issues an interrupt request to the microprocessor 1 via the system bus 4 each time the count value reaches a predetermined value. The microprocessor 1 executes a predetermined program in response to the interrupt request, whereby the microprocessor 1 controls the printer engine 19.

The system clock 16 of the microprocessor 1 is output by the 1/2 frequency divider 7 as in the first embodiment, and the system clock 16 is frequency-modulated. The system clock 16 includes a memory controller 2, a timer controller 8 and a DMA controller 1.
7, input to the input / output ports 21 and 22. Also in the present embodiment, the frequency modulation described above reduces the influence of EMI as in the first embodiment.

On the other hand, since the crystal oscillator 9 is connected only to the timer controller 8 and the parallel / serial converter 18, the output line of the crystal oscillator 9 can be shortened. Therefore, harmonics are not easily emitted from the periphery of the crystal oscillator 9, and the crystal oscillator 9 is a stable oscillation source.
Strict time control can be performed in this device.

As described above, according to the present embodiment, it is possible to achieve a laser beam printer in which time management can be strictly performed and the influence of EMI is small. The present invention may be applied to a system including a plurality of devices or an apparatus including a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0030]

As described above, according to the present invention,
By modulating the frequency of the system clock and performing data processing based on the information from the timer circuit that includes a stabilized oscillator, it is possible to reduce the unnecessary electromagnetic field emitted and to perform strict time management. it can.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a personal computer according to a first embodiment of the present invention.

FIG. 2 is an example of a high frequency spectrum emitted from a clock line.

FIG. 3 is an example of a high frequency spectrum emitted from a frequency modulated clock line.

FIG. 4 is a configuration block diagram of a laser beam printer according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Microprocessor 2 Memory Controller 3 Semiconductor Memory 4 System Bus 5 Low Frequency Oscillator 6 Voltage Controlled Oscillator (VCO) 7 1/2 Divider 8 Timer Controller 9 Crystal Oscillator 10 CRT Controller 11 CRT Display 12 Input / Output Port 13 Keyboard 14 Hard disk controller 15 Hard disk drive 16 System clock 17 DMA controller 18 Parallel-serial converter 19 Printer engine 21, 22 Input / output port 24 External computer device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A microprocessor and a plurality of control units which are controlled by the microprocessor, wherein the microprocessor and the control unit operate by receiving supply of a predetermined clock pulse via a bus-type signal line. In the electronic device, a means for frequency-modulating a high-frequency signal with a low-frequency signal, a means for dividing the frequency-modulated signal by 1 / n (n is an integer) to generate the clock pulse, and a constant period Oscillating means for generating the signal of, a means for counting the signal of the constant period, and means for generating an interrupt to the microprocessor based on the counting result, the microprocessor is synchronized with the interrupt An electronic device characterized by being operated by. 2. The electronic device according to claim 1, wherein the microprocessor executes image processing by using the clock pulse as a reference clock for image formation.