Abstract:
A spectrum analyzer includes: two sets of measuring units having mixers, local oscillators, and IF sections for separately measuring frequency characteristics of two input signals; a trigger control section which generates a trigger signal for specifying a measurement start timing in each of the two sets of measuring units; a sweep control section which simultaneously sends an instruction to the two local oscillators when a trigger signal is inputted and performs a sweep control so that the two local oscillators output local oscillation signals of the same frequency at the same timing. This provides a frequency characteristics measuring device which can simplify the configuration for performing a measurement and reduce the undue effort required for the measurement.

Description:
TECHNICAL FIELD 
     The present invention relates to a frequency characteristics measuring device for measuring a frequency characteristic or the like of an input signal in a spectrum analyzer or the like. 
     BACKGROUND ART 
     A spectrum analyzer is conventionally known which measures a frequency characteristic of an input signal by performing frequency sweep (see, for example, Patent Document 1). The spectrum analyzer has input terminals in two lines and measures a frequency characteristic of a signal input through one of the input terminals. The measured frequency characteristic is displayed through a display section.
     Patent Document 1: Japanese Patent Laid-Open No. 8-233875 (pp. 3-4,  FIGS. 1-2 )   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The conventional spectrum analyzer disclosed in Patent Document 1 for example has two input terminals but performs measurement of a frequency characteristic with respect to a signal input through one of the two input terminals. Therefore, simultaneously making measurements of frequency characteristics of two kinds of signals requires two spectrum analyzers and an externally attached trigger device for generating a trigger signal for synchronization of the measurements, and there is a problem that the configuration for measurement is complicated and considerable amounts of time and work are required for measurement. As a method of comparing frequency characteristics of two kinds of signals, a method of printing and comparing corresponding measurement results is conceivable. This method, however, has a problem that it is difficult to perform analysis with accuracy. As another method of comparing frequency characteristics of two kinds of signals, a method of capturing frequency characteristics of two kinds of signals obtained by measurement in an external analysis device (external computer) and making comparison by performing data processing thereon is conceivable. This method requires the provision of an analysis device and performing an analysis operation separately from measurement and therefore has a problem that the configuration for measurement is further complicated and considerable amounts of time and work are required for measurement. 
     The present invention has been created in consideration of these points and an object of the present invention is to provide a frequency characteristic measuring device capable of simplifying the configuration for measurement and reducing the amounts of time and work required for measurement. 
     Solution to Problem 
     To solve the above-described problems, the present invention provides a frequency characteristics measuring device having a plurality of measuring units which respectively measure frequency characteristics of a plurality of input signals, a trigger control unit which outputs a plurality of trigger signals designating measurement start timing in each of the plurality of measuring units, and a sweep control unit which controls frequency sweep operations in each of the plurality of measuring units in synchronization with the plurality of trigger signals output from the trigger control unit. Making measurements on a plurality of input signals in parallel with each other in synchronization with a trigger signal internally generated is thereby enabled and the need for a device externally connected is eliminated. Consequently, the configuration for measurement can be simplified and the amounts of time and work required for measurement can be reduced. 
     It is desirable that each of the above-described plurality of measuring units include a local oscillator whose oscillation frequency can be changed, and a mixer which mixes a local oscillation signal output from the local oscillator and a signal inputted through an input terminal and outputs the mixed signals; a state signal indicating the operating state of the local oscillator be output from the local oscillator; and the sweep control unit perform control of the frequency sweep operation in the measuring unit including the local oscillator regarded as being in an operational state according to a notice given by means of the state signal. In this way, frequency sweep control can be performed by checking the frequency-sweepable state. 
     It is desirable that the above-described sweep control unit have a selecting unit which selects any one of the plurality of trigger signals, and a plurality of sweep units which individually control the frequency sweep operations in each of the plurality of measuring units in synchronization with the one trigger signal selected by the selecting unit. This enables frequency sweep to be started by the same timing in the plurality of measuring units. In this way, timing of measurement of frequency characteristics can be easily adjusted. 
     It is desirable that the above-described sweep control unit have a plurality of selecting units which select the plurality of trigger signals so as not to doubly select any of the trigger signals, and a plurality of sweep units which individually control the frequency sweep operations in the plurality of measuring units respectively in synchronization with the trigger signals selected by the plurality of selecting units. This enables the measuring operations in a plurality of systems to be independently performed as in the case of using a plurality of frequency characteristic measuring devices. 
     It is desirable that the above-described sweep control unit have a selecting unit which selects any one of the plurality of trigger signals, a plurality of sweep units to which one of the trigger signals selected by the selecting unit is input, and which individually control the frequency sweep operations in each of the plurality of measuring units in synchronization with the trigger signal, and a trigger input limiting unit which permits input of the trigger signal to the plurality of sweep units when all the state signals respectively corresponding to the plurality of measuring units indicate being in the operational state. The trigger signal is thereby input to each sweep unit when frequency sweep can be performed in all the measuring units, so that measurements in the two systems can be simultaneously started with improved reliability. 
     It is desirable that each of the above-described plurality of sweep units perform operations to control the frequency sweep operations in each of the plurality of measuring units when all the state signals respectively corresponding to the plurality of measuring units indicate being in the operational state. This enables stopping frequency sweep in all the measuring units when frequency sweep cannot be performed in a part of the measuring units. Consequently, not only timing of starts of measurement in the plurality of measuring units but also timing of the operations during frequency sweep can be reliably adjusted. 
     It is desirable that the above-described sweep control unit have a selecting unit which selects any one of the plurality of trigger signals, a plurality of sweep units to which one of the trigger signals selected by the selecting unit is input, and which individually control the frequency sweep operations in each of the plurality of measuring units in synchronization with the trigger signal, and a delay unit which delays timing of input of the trigger signal by a predetermined length of time with respect to part of the plurality of measuring units. In this way, timing of inputting of the trigger signal to the plurality of sweep units can be made different from each other by a predetermined length of time with accuracy to set a time difference with accuracy between moments at which frequency sweep is started when measurement is performed in the plurality of systems. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a spectrum analyzer in an embodiment of the present invention. 
         FIG. 2  is a diagram showing in detail the configuration of the sweep control section in accordance with case  1 . 
         FIG. 3  is a diagram showing in detail the configuration of the sweep control section in accordance with case  1 . 
         FIG. 4  is a diagram showing in detail the configuration of the sweep control section in accordance with case  2 . 
         FIG. 5  is a diagram showing in detail the configuration of the sweep control section in accordance with case  3 . 
         FIG. 6  is a diagram showing in detail the configuration of the sweep control section in accordance with case  4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A spectrum analyzer which is a frequency characteristics measuring device according to an embodiment of the present invention will be described in detail with reference to the drawings.  FIG. 1  is a diagram showing the configuration of a spectrum analyzer in an embodiment of the present invention. As shown in  FIG. 1 , the spectrum analyzer  10  in the present embodiment includes mixers  110  and  210 , local oscillators  112  and  212 , IF sections (intermediate frequency processing sections)  120  and  220 , a sweep control section  300 , a trigger control section  350 , a CPU  400 , a display section  410 , and an operation section  420 . 
     The spectrum analyzer  10  in the present embodiment has two input terminals IN 1  and IN 2  through which measurement target signals (signals to be measured) are input and a trigger terminal TG through which an external trigger signal is input. The spectrum analyzer  10  simultaneously measures frequency characteristics of two measurement target signals fin 1  and fin 2  input through these two input terminals IN 1  and IN 2 , and displays spectrums as measurement results. 
     The mixer  110 , the local oscillator  112  and the IF section  120  are provided with the spectrum analyzer  10  to measure frequency characteristics of the measurement target signal fin 1  input through one input terminal IN 1 . The mixer  110  is supplied with the measurement target signal fin 1  input through one input terminal IN 1  and a local oscillation signal f osc1  output from the local oscillator  112 , and outputs a signal which is a mixture of the measurement target signal fin 1  and the local oscillation signal f osc1 . The local oscillator  112  outputs the local oscillation signal f osc1  whose oscillation frequency is sweepable through a predetermined range. For example, the local oscillator  112  is constituted by a PLL circuit including a variable frequency divider, a phase comparator, a VCO (voltage-controlled oscillator). To broaden the variable frequency range of the local oscillation signal output from the local oscillator  112 , a plurality of VCOs having different variable frequency ranges are ordinarily used. When the frequency of the local oscillation signal is changed in one direction, the VCO to be used is changed (band selection is made). 
     The IF section  120  performs analog signal processing and digital signal processing on the output signal from the mixer  110  to perform measurement of frequency characteristics of the measurement target signal fin 1 . The IF section  120  includes an intermediate frequency filter  122 , an ADC (analog-to-digital converter)  124  and a DSP (digital signal processor)  126 . The intermediate frequency filter  122  is a band-pass filter which allows only a predetermined intermediate frequency component (intermediate frequency signal) in the output signal from the mixer  110  to pass therethrough. The ADC  124  converts the intermediate frequency signal output from the intermediate frequency filter  122  into digital data at a predetermined sampling frequency. The DSP  126  performs various kinds of signal processing on the intermediate frequency signal converted into digital data to measure characteristic values (e.g., the signal level and the bit error rate) of the intermediate frequency signal. More specifically, the DSP  126  performs processing including detection processing and image removal processing on the intermediate frequency signal. 
     Similarly, the mixer  210 , the local oscillator  212  and the IF section  220  are provided with the spectrum analyzer  10  to measure frequency characteristics of the measurement target signal fin 2  input through the other input terminal IN 2 . The mixer  210  is supplied with the measurement target signal fin 2  input through the other input terminal IN 2  and a local oscillation signal f OSC2  output from the local oscillator  212 , and outputs a signal which is a mixture of the measurement target signal fin 2  and the local oscillation signal f OSC2 . The local oscillator  212  outputs the local oscillation signal f OSC2  whose oscillation frequency is sweepable through a predetermined range. For example, the local oscillator  212  is constituted by a PLL circuit including a variable frequency divider, a phase comparator, a VCO (voltage-controlled oscillator), as is the local oscillator  112 . To broaden the variable frequency range of the local oscillation signal output from the local oscillator  212 , a plurality of VCOs having different variable frequency ranges are ordinarily used. When the frequency of the local oscillation signal is changed in one direction, the VCO to be used is changed (a band selection is made). 
     The IF section  220  performs analog signal processing and digital signal processing on the output signal from the mixer  210  to perform measurement of frequency characteristics of the measurement target signal fin 2 . The IF section  220  includes an intermediate frequency filter  222 , an ADC  224  and a DSP  226 . The intermediate frequency filter  222  is a band-pass filter which allows only a predetermined intermediate frequency component (intermediate frequency signal) in the output signal from the mixer  210  to pass therethrough. The ADC  224  converts the intermediate frequency signal output from the intermediate frequency filter  222  into digital data by sampling at a predetermined sampling frequency. The DSP  226  performs various kinds of signal processing on the intermediate frequency signal converted into digital data to measure characteristic values of the intermediate frequency signal. More specifically, the DSP  226  performs processing including demodulation processing and image removal processing on the intermediate frequency signal. 
     Only the essential portion of the configuration necessary for measurement of frequency characteristics has been described. In actuality, however, attenuators are provided between the input terminal IN 1  and the mixer  110  and between the input terminal IN 2  and the mixer  210  to perform signal level adjustment. Also, in actuality, a combination of a mixer and a local oscillator or a plurality of combinations of mixers and local oscillators are added to perform image removal processing. The configuration necessary for frequency measurement can be changed as desired according to required specifications. 
     The sweep control section  300  is supplied with two kinds of trigger signals T 1  and T 2  and LO 1 redy and LO 2 redy signals respectively output from the local oscillators  112  and  212 , and sends sweep signals S 1  and S 2  to the two local oscillators  112  and  212 , respectively, thereby performing sweep control on each of the two local oscillators  112  and  212 . The LO 1 redy signal is a signal indicating the state of operation of the local oscillator  112 . For example, the LO 1 redy signal becomes high level at the time of entering in a sweepable state (enabled state). For example, in a situation where a band selection is made by changing the VCO during frequency sweep, the LO 1 redy signal becomes low level when this band selection is being made. The LO 1 redy signal again becomes high level when the band selection is completed. The same applies to the LO 2 redy signal. 
     The trigger control section  350  generates the trigger signals T 1  and T 2  each instructing a start of measurement. The trigger signals T 1  and T 2  are generated in synchronization with an external trigger signal input through the trigger terminal TG, IF trigger signals output from the IF sections  120  and  220 , video trigger signals or the like. 
     The CPU  400  performs overall control of the spectrum analyzer  10  and performs processing for simultaneously displaying through the display section  410  the two measurement results (characteristic values) output from the IF sections  120  and  220  and processing for setting a measurement condition according to a command from a user using the operation section  420 . The operation section  420  is provided with a plurality of components such as switches and operating variable resistors to be operated by a user. A user enters a command to set a measurement condition, a command to start measuring, a command to stop measuring and other commands by operating the switches, the operating variable resistors or the like provided in the operation section  420 . 
     A concrete example of the generation of the sweep signals S 1  and S 2  by the sweep control section  300  on the basis of the trigger signals T 1  and T 2  output from the trigger control section  350  will next be described. Concrete examples of the sweep control section  300  realizing, for example, four cases (cases 1 to 4) described below will be described. 
     (Case 1) 
       FIG. 2  is a diagram showing in detail the configuration of the sweep control section  300  in accordance with case  1 . The sweep control section  300  shown in  FIG. 2  includes two sweep sections  310  and  312  and two switch sections  320  and  322 . The sweep section  310  outputs the sweep signal S 1  necessary for sweeping the frequency of the local oscillator  112 . In case where the local oscillator  112  is constituted by a PLL circuit including a variable frequency divider, a phase comparator and a VCO as described above, the sweep section  310  generates the sweep signal S 1  instructing a start and an end of the sweep operation by which the division ratio of the variable frequency divider is changed in one direction, and outputs the sweep signal S 1 . The sweep signal S 1  is input to the local oscillator  112 . Also, the sweep section  310  is supplied with the LO 1 redy signal input from the local oscillator  112  and the trigger signal T 1  (or T 2 ) input via the switch section  320 . When supplied with the trigger signal T 1  or the like when the LO 1 redy signal is high level, the sweep section  310  starts outputting the sweep signal S 1 . The sweep signal S 1  is also input to the IF section  120  to notify the IF section  120  of the start and end of sweep control. 
     Similarly, the sweep section  312  outputs the sweep signal S 2  necessary for sweeping the frequency of the local oscillator  212 . In case where the local oscillator  212  is constituted by a PLL circuit including a variable frequency divider, a phase comparator and a VCO, the sweep section  312  generates the sweep signal S 2  instructing a start and an end of the sweep operation by which the division ratio of the variable frequency divider is changed in one direction, and outputs the sweep signal S 2 . The sweep signal S 2  is input to the local oscillator  212 . Also, the sweep section  312  is supplied with the LO 2 redy signal input from the local oscillator  212  and the trigger signal T 2  (or T 1 ) input via the switch section  322 . When supplied with the trigger signal T 2  or the like when the LO 2 redy signal is high level, the sweep section  312  starts outputting the sweep signal S 2 . The sweep signal S 2  is also input to the IF section  220  to notify the IF section  220  of the start and end of sweep control. 
     The switch section  320  selectively outputs one of the two trigger signals T 1  and T 2  toward the sweep section  310 . The switch section  322  selectively outputs one of the two trigger signals T 1  and T 2  toward the sweep section  312 . In the example shown in  FIG. 2 , the trigger signal T 1  is selected in the switch section  320  to be input to the sweep section  310 . Also, the trigger signal T 2  is selected in the switch section  322  to be input to the sweep section  312 . 
     Setting the switching states (selecting states) of the two switch sections  320  and  322  in the above-described way enables the measurement of the frequency characteristics of the measurement target signal fin 1  input from one input terminal IN 1  to be measured in synchronization with the trigger signal T 1  and enables the measurement of the frequency characteristics of the measurement target signal fin 2  input from the other input terminal IN 2  to be measured in synchronization with the trigger signal T 2 . The measuring operations in the two systems can be performed independently of each other. 
     It is also possible to perform the measuring operations in the two systems in synchronization with one trigger signal T 1  (or T 2 ) by changing the switching states of the switch sections  320  and  322 .  FIG. 3  shows in detail the configuration of the sweep control section  300  in a case where the switching state of the switch section  322  is changed. The configuration shown in  FIG. 3  is the same as that shown in  FIG. 2  except for changing only the switching state of the switch section  322 . 
     In the example shown in  FIG. 3 , the trigger signal T 1  is selected in the switch section  320  to be input to the sweep section  310 , and the trigger signal T 1  is selected in the switch section  322  to be input to the sweep section  312 . That is, one trigger signal T 1  is selected by two switch sections  320  and  322  to be input to the two sweep sections  310  and  312 . Accordingly, the times at which the sweep signals S 1  and S 2  are output from the sweep sections  310  and  312  coincide with each other and it is possible to make measurements in the two systems in synchronization with one trigger signal T 1 . Sweep control performed in synchronization with an IF trigger signal output according to the IF level (intermediate frequency signal level) of bursts, for example, when high-frequency components of the bursts are measured has conventionally been practiced. In the conventional art, sweep control cannot be performed if the IF level is so low that the IF trigger signal cannot be produced. However, the configuration shown in  FIG. 3  enables measurement of harmonic waves of bursts in synchronization with the trigger signal T 1  as well as measurement of the fundamental wave of bursts in synchronization with the same trigger signal T 1 . 
     (Case 2) 
       FIG. 4  is a diagram showing in detail the configuration of the sweep control section  300  in accordance with case  2 . The sweep control section  300  shown in  FIG. 4  includes two sweep sections  310  and  312 , two switch sections  320  and  322 , and three AND circuits  330 ,  332 , and  334 . The configuration shown in  FIG. 4  differs from the configuration shown in  FIG. 3  in that three AND circuits  330 ,  332 , and  334  are added. Description will be made below by noting mainly this point of difference. 
     The AND circuit  330  is inserted between the switch section  320  and the sweep section  310 . The trigger signal T 1  output from the switch section  320  is input to one input end of the AND circuit  330 , while an output end of the AND circuit  334  is connected to the other input end of the AND circuit  330 . The AND circuit  332  is inserted between the switch section  322  and the sweep section  312 . The trigger signal T 1  output from the switch section  322  is input to one input end of the AND circuit  332 , while the output end of the AND circuit  334  is connected to the other input end of the AND circuit  332 . The AND circuit  334  has the LO 1 redy signal and the LO 2 redy signal input to its two input ends, respectively, and outputs a signal representing the logical product of the LO 1 redy signal and the LO 2 redy signal. That is, the AND circuit  334  outputs a high level signal when both the LO 1 redy signal and the LO 2 redy signal are in an enabled state (high level). 
     The example shown in  FIG. 4  has in common with the example shown in  FIG. 3  a feature which resides in inputting the trigger signal T 1  to the two sweep sections  310  and  312 , but differs from the example shown in  FIG. 3  in that inputting of the trigger signal T 1  to the two sweep sections  310  and  312  is not performed unless both the LO 1 redy signal and the LO 2 redy signal are high level. That is, only when both the two local oscillators  112  and  212  are operational, the trigger signal T 1  is input to the two sweep sections  310  and  312  to enable outputting the sweep signals S 1  and S 2  simultaneously with each other from the two sweep sections  310  and  312  in synchronization with the trigger signal T 1 , thus enabling measurements on the measurement target signals to be simultaneously started with improved reliability. 
     While outputting of the two sweep signals S 1  and S 2  in synchronization with the trigger signal T 1  has been described, the two sweep signals S 1  and S 2  may be output in synchronization with the trigger signal T 2 . 
     (Case 3) 
       FIG. 5  is a diagram showing in detail the configuration of the sweep control section  300  in accordance with case  3 . The sweep control section  300  shown in  FIG. 5  includes two sweep sections  310  and  312 , two switch sections  320  and  322 , and three AND circuits  330 ,  332 , and  334 . The configuration shown in  FIG. 5  differs from the configuration shown in  FIG. 4  in input routing of the LO 1 redy signal and the LO 2 redy signal. Description will be made below by noting mainly this point of difference. 
     More specifically, the example shown in  FIG. 5  differs from the example shown in  FIG. 4  in that the output signal from the AND circuit  334  (the signal representing the logical product of the LO 1 redy signal and the LO 2 redy signal) is input to the sweep section  310  in place of the LO 1 redy signal, and that the output signal from the AND circuit  334  is input to the sweep section  312  in place of the LO 2 redy signal. That is, the two sweep sections  310  and  312  are operational only when both the LO 1 redy signal and the LO 2 redy signal are high level, and the trigger signal T 1  (or T 2 ) is input to the sweep sections  310  and  312  only when both the LO 1 redy signal and the LO 2 redy signal are high level. Accordingly, when only one of the local oscillators, e.g., the local oscillator  112  is made non-operational (disabled state) by band selection, outputting of the sweep signal S 1  from the sweep section  310  and outputting of the sweep signal S 2  from the sweep section  312  are simultaneously stopped to simultaneously stop making measurements in the two systems. Thereafter, when band selection in the local oscillator  112  is completed, the measurements in the two systems can be restarted simultaneously by restarting outputting of the sweep signal S 1  and outputting of the sweep signal S 2  by the same timing. Thus, not only timing of starts of measurement in the two systems but also timing of the operations during frequency sweep can be reliably adjusted. 
     (Case 4) 
       FIG. 6  is a diagram showing in detail the configuration of the sweep control section  300  in accordance with case  4 . The sweep control section  300  shown in  FIG. 6  includes two sweep sections  310  and  312 , a switch section  320 , and a delay section (D)  340 . The configuration shown in  FIG. 6  differs from the configuration shown in  FIG. 2  in that the switch section  322  is removed and the delay section  340  is added. Description will be made below by noting mainly this point of difference. 
     More specifically, the trigger signal T 1  (or T 2 ) selectively output from the switch section  320  is directly input to the sweep section  310  and is also input to the sweep section  312  via the delay section  340 . The delay section  340  delays the trigger signal T 1  (or T 2 ) by a predetermined length of time t and thereafter outputs the trigger signal. This length of time t can be arbitrarily set within a predetermined range. For example, the length of time t is set by the CPU  400 . In this way, timing of inputting of the trigger signal T 1  to the sweep section  310  and timing of inputting of the trigger signal T 1  to the sweep section  312  can be made different from each other by the length of time t with accuracy to set a time difference accurately equal to the length of time t between moments at which frequency sweep is started when measurement is performed in the two systems. 
     The above-described mixers  110  and  210 , local oscillators  112  and  212  and IF sections  120  and  220  correspond to the plurality of measuring units; the trigger control section  350  corresponds to the trigger control unit; and the sweep control section  300  corresponds to the sweep control unit. Also, the switch sections  320  and  322  correspond to the selecting unit; the sweep sections  310  and  312  correspond to the sweep units; the AND circuits  330 ,  332 , and  334  correspond to the trigger input limiting unit; and the delay section  340  corresponds to the delay unit. 
     The present invention is not limited to the above-described embodiment. Various changes and modifications may be made in the embodiment within the scope of the present invention. Of the above-described embodiment, details of the configurations of the sweep control section  300  in accordance with cases 1 to 4 have been individually shown with reference to  FIGS. 2 to 6 , respectively. However, one sweep control section  300  may have all or some of those configurations. 
     While in the above-described embodiment two identical combinations of components are provided to simultaneously measure frequency characteristics of two input signals, three or more identical combinations of components may be provided to simultaneously measure frequency characteristics of three or more input signals. 
     While two DSPs  126  and  226  are provided in the above-described embodiment, one DSP  126  may perform the processing for the other DSP  226  if its throughput is sufficiently high, and the other DSP  226  may be removed. The manufacturing cost can be reduced by reducing the number of component parts in this way. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, measurements can be made in parallel with each other on a plurality of input signals in synchronization with a trigger signal internally generated and the need for an externally connected device is eliminated, so that the configuration for measurement can be simplified and the amounts of time and work required for measurement can be reduced. 
     REFERENCE SIGNS LIST 
     
         
           10  Spectrum analyzer 
           110 ,  210  Mixer 
           112 ,  212  Local oscillator 
           120 ,  220  IF section (intermediate frequency processing section) 
           122 ,  222  Intermediate frequency filter 
           124 ,  224  ADC (analog-digital converter) 
           126 ,  226  DSP (digital signal processor) 
           300  Sweep control section 
           310 ,  312  Sweep section 
           320 ,  322  Switch section 
           330 ,  332 ,  334 AND circuit 
           340  Delay section 
           350  Trigger control section 
           400  CPU 
           410  Display section 
           420  Operation section