Abstract:
The timer control circuit includes plurality of timers that perform predetermined count operations. The signal selection circuit section allows to selectively pass underflow signals supplied from the timers based on the control signals. The flip-flop is supplied with an output of the signal selection circuit section a toggle signal.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a timer control circuit for controlling an output of a timer incorporated in a computer such as a microcomputer. More particularly, the present invention relates to a timer control circuit capable of providing a complicated output waveform without casting a burden upon software.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventionally, there is known the circuit shown in FIG. 5 that outputs signals of various waveforms from an external output terminal of a microcomputer by using an output signal of a timer incorporated in the microcomputer.  
           [0003]    This circuit includes timers T 1 , T 2  and T 3 , flip-flops (“F/F”) F 1 , F 2  and F 3 , and switches S 1  to S 6 . The generated signal is output from the F/Fs F 1 , F 2  and F 3 . The timers T 1 , T 2  and T 3  are set in mode so as to automatically conduct down counting for two periods. Initial count values in the first and second periods are set to different values.  
           [0004]    In the circuit shown in FIG. 5 the F/F are toggle changed based on underflow or overflow signal output from the respective timers T 1 , T 2  and T 3  when counting corresponding to one period is finished.  
           [0005]    For example, when the timer T 1  is started, it begins counting as shown in FIG. 6. If the switch S 1  is ON at two time points t 1  and t 2  when the timer T 1  has output an underflow signal, then an output signal of the flip-flop F 1  is inverted and an output signal of one shot pulse can be generated.  
           [0006]    Furthermore, a complicated waveform including two pulses maybe output by using any of the following two methods.  
           [0007]    Method 1: This is a method used when one timer is provided for one flip-flop. For example, as shown in FIG. 5, only one timer T 1  is connected to the flip-flop F 1 . When the timer T 1  is started it begins counting as shown in FIG. 7. If the switch S 1  is ON at two time points t 1  and t 2  when the timer T 1  has output an underflow signal, then an output signal of the flip-flop F 1  is inverted and an output signal of one shot pulse can be generated. Thereafter, the count value of the timer T 1  is re-set, and the timer T 1  is started again. As a result, the output signal of the flip-flop F 1  is inverted at two time points t 3  and t 4  when the timer T 1  has output an underflow signal, and a second pulse having a different width can be output.  
           [0008]    Method 2: This is a method used when two or more timers are provided with one flip-flop. For example, as shown in FIG. 5, three timers T 1 , T 2  and T 3  are connected to the flip-flop F 2 . When the timers T 1  and T 2  are simultaneously started, the switch S 2  is set ON. As shown in FIG. 8, the timers T 1  and T 2  begin counting. At a time point t 1 , the timer T 1  outputs a first underflow signal, and an output of the flip-flop F 2  is inverted. Subsequently, the switch S 3  is changed over to the ON state. If thereafter two underflow signals have been output from the timer T 2 , then the switch S 2  is changed over to the ON state. As a result, the output of the flip-flop F 2  is inverted at a time point t 2  when a first underflow signal has been output from the timer T 2 . Furthermore, at a time point t 3  when a second underflow signal has been output from the timer T 2 , the output of the flip-flop F 2  is inverted. Thereafter, the timer T 1  causes second underflow, and the output of the flip-flop F 2  is inverted at a time point t 4 . As a result, a two-pulse waveform as shown in FIG. 4 is generated. Thus in this technique, an output waveform as shown in FIG. 8 is obtained by selecting one among a plurality of timers by using switches.  
           [0009]    Thus, in the conventional timer control circuit, one timer is started a plurality of times or one of a plurality of timers is selected when generating a complicated output waveform including two or more pulses. Therefore, changeover of the switches S 1  to S 6  and counter re-setting need to be conducted by software in a personal computer. This is disadvantageous because it increases a load of the software.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of this invention to provide a timer control circuit capable of simply providing a desired out put waveform without burdening the software with a load even in the case of a complicated waveform.  
           [0011]    The timer control circuit of one aspect of this invention comprises a plurality of timers. Each timer counts up to a predetermined value and outputs an underflow signal when counting is over. Furthermore, a logic unit receives a control signal and the underflow signals from all of the timers, and based on the control signal passes one of the underflow signals as a toggle signal. Furthermore, a control unit receives the toggle signal from the logic unit. The control unit changes its output state based on the input timing of the toggle signal.  
           [0012]    The timer control circuit of another aspect of this invention comprises a plurality of timers. Each timer counts up to a predetermined value, generates and outputs an enable during counting, and outputs an underflow signal when counting is over. Furthermore, a plurality of logic units commonly receive an underflow signal output from one of the timers and an enable signal output from at least one of the timers. Each logic unit receives a control signal and the underflow signals from some of the timers and based on the control signal passes one of the underflow signals as a toggle signal only during an effective interval of the enable signal(s). Furthermore, there are provided a plurality of control units. Each control unit receives the toggle signal from corresponding one of the logic units. Each control unit changes its output state based on the input timing of the toggle signal.  
           [0013]    The timer control circuit of still another aspect of this invention comprises a plurality of timers. Each timer counts up to a predetermined value and outputs an overflow signal when counting is over. Furthermore, a logic unit receives a control signal and the overflow signals from all of the timers, and based on the control signal passes one of the overflow signals as a toggle signal. Furthermore, a control unit receives the toggle signal from the logic unit. The control unit changes its output state based on the input timing of the toggle signal.  
           [0014]    The timer control circuit of still another aspect of this invention comprises a plurality of timers. Each timer counts up to a predetermined value, generates and outputs an enable during counting, and outputs an overflow signal when counting is over. Furthermore, a plurality of logic units commonly receive an overflow signal output from one of the timers and an enable signal output from at least one of the timers. Each logic unit receives a control signal and the overflow signals from some of the timers and based on the control signal passes one of the overflow signals as a toggle signal only during an effective interval of the enable signal(s). Furthermore, a plurality of control units are provided. Each control unit receives the toggle signal from corresponding one of the logic units. Each control unit changes its output state based on the input timing of the toggle signal.  
           [0015]    Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a circuit block diagram showing a first embodiment of a timer control circuit according to the present invention;  
         [0017]    [0017]FIG. 2 is a time chart showing operation of the first embodiment;  
         [0018]    [0018]FIG. 3 is a circuit block diagram showing a second embodiment of a timer control circuit according to the present invention;  
         [0019]    [0019]FIG. 4 is a time chart showing operation of the first embodiment;  
         [0020]    [0020]FIG. 5 is a circuit block diagram showing a configuration of a conventional timer output signal control circuit;  
         [0021]    [0021]FIG. 6 is a time chart showing operation of a conventional technique of FIG. 5;  
         [0022]    [0022]FIG. 7 is another time chart showing operation of the conventional technique of FIG. 5; and  
         [0023]    [0023]FIG. 8 is still another time chart showing operation of the conventional technique of FIG. 5. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Embodiments of the timer control circuit according to the present invention will be described in detail below while referring to the accompanying drawings.  
         [0025]    [0025]FIG. 1 is a diagram showing a first embodiment of a timer control circuit according to the present invention. This timer control circuit includes plurality of timers T 1  to T 3 , signal selection logic circuit section  5 , and plurality of flip-flops F 1  to F 3 . The flip-flops F 1  to F 3  are, for example, flip-flops of set reset (SR) type. Output signals of the signal selection logic circuit section  5  are input to the flip-flops F 1  to F 3  as toggle signals. Control signals C 1  to C 7  input to the signal selection logic circuit section  5  are output from a circuit included in the personal computer.  
         [0026]    The timers T 1 , T 2  and T 3  are incorporated in the microcomputer. In this case, the timers T 1 , T 2  and T 3  are set in mode so as to automatically conduct down counting for two periods in the same way as the foregoing description. Initial count values in the first and second periods are set to different values.  
         [0027]    The signal selection logic circuit section  5  includes a signal selection circuit section  10  for the flip-flop F 1 , a signal selection circuit section  20  for the flip-flop F 2 , and a signal selection circuit section  30  for the flip-flop F 3 .  
         [0028]    The signal selection circuit section  10  includes an AND circuit  11  for passing/blocking an output of the timer T 1  according to the control signal C 1 , an AND circuit  12  for passing/blocking an output of the timer T 2  according to the control signal C 2 , and an OR circuit  13  for deriving a logical sum of outputs of the AND circuits  11  and  12 .  
         [0029]    The signal selection circuit section  20  includes an AND circuit  21  for passing/blocking the output of the timer T 1  according to the control signal C 3 , an AND circuit  22  for passing/blocking the output of the timer T 2  according to the control signal C 4 , an AND circuit  23  for passing/blocking an output of the timer T 3  according to the control signal C 5 , and an OR circuit  24  for deriving a logical sum of outputs of the AND circuits  21 ,  22  and  23 .  
         [0030]    The signal selection circuit section  30  includes an AND circuit  31  for passing/blocking an output of the timer T 2  according to the control signal C 6 , an AND circuit  32  for passing/blocking an output of the timer T 3  according to the control signal C 7 , and an OR circuit  33  for deriving a logical sum of outputs of the AND circuits  31  and  32 .  
         [0031]    Operation of the timer control circuit according to the first embodiment will now be described by referring to FIG. 2. FIG. 2 shows the output of the flip-flop F 1  and signals relating to the output.  
         [0032]    In this case, both of the control signals C 1  and C 2  are set to high logical level (“H”). In other words, the control signals C 1  and C 2  are fixed to “H” when the flip-flop F 1  is used. It is not necessary to especially conduct “H” and low logical level (“L”) changeover control according to a signal waveform to be output.  
         [0033]    Subsequently, the timers T 1  and T 2  are started simultaneously (at time t 1 ). The timers T 1  and T 2  begin counting. Thereafter, at time t 2 , down counting of a first period of the timer T 1  is finished and the timer T 1  outputs an underflow signal. At this time, the control signal C 1  is “H”. Therefore, the underflow signal supplied from the timer T 1  is input to the flip-flop F 1 . As a result, an output signal of the flip-flop F 1  is inverted (the time t 2 ). By the way, the timer T 1  begins down count operation of a second period at the time t 2 .  
         [0034]    Subsequently, at time t 3 , down counting of a first period of the timer T 2  is finished, and the timer T 2  outputs an underflow signal. At this time, the control signal C 2  is “H”. Therefore, the underflow signal supplied from the timer T 2  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 3 ). By the way, the timer T 2  begins down count operation of a second period at the time t 3 .  
         [0035]    Subsequently, at time t 4 , the down counting of the second period of the timer T 2  is finished, and the timer T 2  outputs a second underflow signal. At this time, the control signal C 2  is “H”. Therefore, the second underflow signal supplied from the timer T 2  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 4 ).  
         [0036]    Furthermore, at time t 5 , the down counting of the second period of the timer T 1  is finished, and the timer T 1  outputs a second underflow signal. At this time, the control signal C 1  is “H”. Therefore, the second underflow signal supplied from the timer T 1  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 5 ). In this way, a waveform including two pulses as shown in FIG. 2 is formed.  
         [0037]    If it is desired in the configuration of FIG. 1 to invert the output signal of the flip-flop F 1  by only underflow signals supplied from the timer T 1  as represented by an output waveform shown in FIG. 6, it can be accomplished by setting the control signal C 2  to “L” and setting the control signal C 1  to “H”. By doing so, the output signal of the flip-flop F 1  is inverted only when the timer T 1  has generated an underflow signal. Even if the timer T 2  generates an underflow signal, the output signal of the flip-flop F 1  can be prevented from being influenced the output signal of the flip-flop F 1 .  
         [0038]    In the case of the flip-flop F 2 , an output signal of the flip-flop F 2  can be generated by combining underflow signals supplied from three timers T 1 , T 2  and T 3  although illustration of a waveform example is omitted.  
         [0039]    If all desired timers are thus connected to a flip-flop, an arbitrary number of timers can be selected from among the connected timers in order to invert the output signal of the flip-flop.  
         [0040]    Thus in the first embodiment, the signal selection logic circuit  5 , which is hardware, is disposed between the timers and the flip-flops, and simultaneous use of a plurality of timers is made possible. Therefore, it becomes possible to form the complicated waveform by utilizing the timers without burdening software with a load.  
         [0041]    [0041]FIG. 3 is a diagram showing the second embodiment of a timer control circuit according to the present invention. In FIG. 3, T 1 , T 2  and T 3  denote timers, F 1  and F 2  denote flip-flops. C 1  and C 2  denote control signals for the flip-flop F 1 , and C 3  and C 4  denote control signals for the flip-flop F 2 . Numeral  50  denotes a signal selection logic circuit section. A signal EN 1  is an enable signal output from the timer T 1 . This enable signal EN 1  becomes “H” when the timer T 1  is conducting count operation. A signal EN 2  is an enable signal output from the timer T 2 . This enable signal EN 2  becomes “H” when the timer T 2  is conducting count operation. In the second embodiment as well, the timers T 1 , T 2  and T 3  are set in mode so as to automatically conduct down counting for two periods in the same way as the foregoing description. Initial count values in the first and second periods are set to different values.  
         [0042]    The signal selection logic circuit section  50  includes a signal selection circuit section  60  for the flip-flop F 1 , and a signal selection circuit section  70  for the flip-flop F 2 .  
         [0043]    The signal selection circuit section  60  includes an AND circuit  61  for passing/blocking an output of the timer T 1  according to the control signal C 1 , an AND circuit  62  for passing/blocking an output of the timer T 3  according to the control signal C 2  and the enable signal EN 1 , and an OR circuit  63  for deriving a logical sum of outputs of the AND circuits  61  and  62 .  
         [0044]    The signal selection circuit section  70  includes an AND circuit  71  for passing/blocking an output of the timer T 2  according to the control signal C 3 , an AND circuit  72  for passing/blocking the output of the timer T 3  according to the control signal C 3  and the enable signal EN 2 , and an OR circuit  73  for deriving a logical sum of outputs of the AND circuits  71  and  72 .  
         [0045]    Operation of the timer control circuit according to the second embodiment will now be described by referring to FIG. 4. First, all of the control signals C 1  and C 2  for the flip-flop F 1  and the control signals C 3  and C 4  for the flip-flop F 2  are set to “H”. Subsequently, the timers T 1  and T 3  are started simultaneously (at time t 1 ). The timers T 1  and T 3  begin counting, and the enable signal EN 1  output from the timer T 1  becomes “H”.  
         [0046]    Thereafter, at time t 2 , down counting of a first period of the timer T 1  is finished and the timer T 1  outputs an underflow signal. At this time, the control signal C 1  is “H”. Therefore, the underflow signal supplied from the timer T 1  is input to the flip-flop F 1 . As a result, an output signal of the flip-flop F 1  is inverted (the time t 2 ). By the way, the timer T 1  begins down count operation of a second period at the time t 2 .  
         [0047]    Subsequently, at time t 3 , down counting of a first period of the timer T 3  is finished, and the timer T 3  outputs an underflow signal. At this time, the control signal C 2  and the enable signal EN 1  are “H”. Therefore, the underflow signal supplied from the timer T 3  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 3 ). By the way, the timer T 3  begins down count operation of a second period at the time t 3 .  
         [0048]    Subsequently, at time t 4 , the down counting of the second period of the timer T 3  is finished, and the timer T 3  outputs a second underflow signal. At this time, the control signal C 2  and the enable signal EN 1  are “H”. Therefore, the second underflow signal supplied from the timer T 3  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 4 )  
         [0049]    Furthermore, at time t 5 , the down counting of the second period of the timer T 1  is finished, and the timer T 1  outputs a second underflow signal. At this time, the control signal C 1  is “H”. Therefore, the second underflow signal supplied from the timer T 1  is input to the flip-flop F 1 . As a result, the output signal of the flip-flop F 1  is inverted (the time t 5 ). In this way, a two-pulse waveform is formed by the underflow signals supplied from the timers T 1  and T 3  during the enable signal EN 1  supplied from the T 1  being “H”.  
         [0050]    Subsequently, the timers T 2  and T 3  are started simultaneously (at time t 6 ). As a result, the timers T 2  and T 3  begin counting, and the enable signal EN 1  output from the timer T 2  becomes “H”.  
         [0051]    Thereafter, at time t 7 , down counting of a first period of the timer T 2  is finished and the timer T 2  outputs an underflow signal. At this time, the control signal C 3  is “H”. Therefore, the underflow signal supplied from the timer T 1  is input to the flip-flop F 2 . As a result, an output signal of the flip-flop F 2  is inverted (the time t 7 ). By the way, the timer T 2  begins down count operation of a second period at the time t 7 .  
         [0052]    Subsequently, at time t 8 , down counting of a first period of the timer T 3  is finished, and the timer T 3  outputs an underflow signal. At this time, the control signal C 4  and the enable signal EN 2  are “H”. Therefore, the underflow signal supplied from the timer T 3  is input to the flip-flop F 2 . As a result, the output signal of the flip-flop F 2  is inverted (the time t 8 ). By the way, the timer T 3  begins down count operation of a second period at the time t 8 .  
         [0053]    Subsequently, at time t 9 , the down counting of the second period of the timer T 3  is finished, and the timer T 3  outputs a second underflow signal. At this time, the control signal C 4  and the enable signal EN 2  are “H”. Therefore, the second underflow signal supplied from the timer T 3  is input to the flip-flop F 2 . As a result, the output signal of the flip-flop F 2  is inverted (the time t 9 )  
         [0054]    Furthermore, at time t 10 , the down counting of the second period of the timer T 2  is finished, and the timer T 2  outputs a second underflow signal. At this time, the control signal C 3  is “H”. Therefore, the second underflow signal supplied from the timer T 2  is input to the flip-flop F 2 . As a result, the output signal of the flip-flop F 2  is inverted (the time t 10 ). In this way, a two-pulse waveform is formed by the underflow signals supplied from the timers T 2  and T 3  during the enable signal EN 1  supplied from the T 2  being “H”.  
         [0055]    When an output of a timer (the timer T 3  in this case) is used for control of a plurality of flip-flops (F 1  and F 2  in this case) simultaneously, enable signals of timers are not utilized in the first embodiment described earlier. Even in such intervals that neither the timer T 1  nor the timer T 2  is enabled, therefore, the output signals of the flip-flop F 1  and F 2  are inverted by the underflow signal of the timer T 3 . If the enable signals EN 1  and EN 2  of the timers are utilized as in the second embodiment, however, extra signal inversion as described above can be prevented.  
         [0056]    In the second embodiment, the enable signals EN 1  and EN 2  of the timers are thus utilized. Even in the case where a certain timer is used simultaneously for control of a plurality of flip-flops, flip-flops can be prevented from being inverted by extra underflow signals of that timer.  
         [0057]    While flip-flops are inverted by underflow signals of timers in the above described embodiments, overflow signals may also be used.  
         [0058]    According to the timer control circuit of one aspect of the present invention, a logic circuit section implemented as hardware is disposed between a plurality of timers and flip-flops and simultaneous use of a plurality of timers is made possible as heretofore described. Therefore, it becomes possible to form a complicated wave form by utilizing timers, without burdening software with a load.  
         [0059]    Furthermore, the logic circuit section includes a plurality of AND circuits and an OR circuit. As a result, it becomes possible to form a complicated waveform by utilizing timers, without burdening software with a load.  
         [0060]    According to the timer control circuit of another aspect of the present invention, enable signals of the timers are input to a plurality of logic circuit sections, and the underflow signals supplied from the specific timer(s) are passed through the logic circuit sections only during effective intervals of the enable signals. Therefore, outputs of flip-flops are prevented from being inverted by extra underflow signals supplied from the specific timer/s. As a result, a desired signal waveform can be formed simply and efficiently.  
         [0061]    Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.