Abstract:
The present invention provides a fan that has a fan motor and two signal lines including a number-of-rotations switching control signal line and a rotational state outputting signal line, makes the fan motor rotate at a number of rotations determined by a number-of-rotations switching control signal input via the number-of-rotations switching control signal line, outputs the rotational state of the fan motor via the rotational state outputting signal line, and can provide notification of detail data without increasing the number of signal lines. The fan retains data in the data storage section in a non-volatile manner and outputs the data via the conventionally existing rotational state outputting signal line.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a fan having a fan motor and two signal lines including a number-of-rotations switching control signal line and a rotational state outputting signal line, in which the fan motor runs at a number of rotations determined by a number-of-rotations switching control signal input via the number-of-rotations switching control signal line, and the fan outputs the rotational state of the fan motor via the rotational state outputting signal line.  
         [0003]     2. Description of the Related Art  
         [0004]     Various fans have been used for ventilation or air conditioning (see Japanese Patent Laid-Open No. 5-252784 and Japanese Patent Laid-Open No. 5-264080, for example).  
         [0005]     For example, a server has many fans for cooling. To prevent a failure of a fan from leading to insufficient cooling of the system and interruption of the service, such a server has a redundant configuration including more fans than necessary or unitizes the fans to enable active replacement. Furthermore, there is a system that monitors and controls fans and, if a fan fails, immediately notifies the system manager of the failure to permit replacement of the failed fan. A larger server requires more fans, so that each fan has to be monitored and controlled more precisely.  
         [0006]     Most fans used for cooling servers have a number-of-rotations switching control signal line and a rotational state outputting signal line.  
         [0007]     Such a fan outputs the rotational state of the fan motor, and thus, the system can monitor the rotational state to know if the fan motor runs normally at that instant. However, conventional fans provide no detail data as to the manufacturers, the dates of manufacture, when the fans were put into service, or how long the fans have been in service. Therefore, there is a problem that preventive measures cannot be taken, for example, a fan cannot be replaced with a new one based on a prediction that the fan will stop rotating soon.  
         [0008]     Besides, there has been devised a system that unitizes fans and can grasp the performance of the fans by reading additional information, such as a switch-based ID setting (for example, four kinds of outputs represented by two bits), that is set in the unit for differentiating the fans according to their performance. However, additional signal lines for reading the switch-based ID setting have to be provided in the unit, and if multiple IDs are set, the number of signal lines increases. For example, a large server has many fans, and each fan has the number-of-rotations switching control signal line and the rotational state outputting signal line. Thus, such a further increase of the number of signal lines is a problem.  
         [0009]     Alternatively, rather than simply setting an ID in the fan unit, a memory for storing detail data regarding the fans may be provided in the fan unit. However, if signal lines are provided for reading the data from the memory, for the same reason as described above, there arises a problem that the total number of signal lines extremely increases.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made in view of the above circumstances and provides a fan that can provide notification of detail data without increasing signal lines.  
         [0011]     The present invention provides a fan that has a fan motor and two signal lines including a number-of-rotations switching control signal line and a rotational state outputting signal line, in which the fan motor rotates at a number of rotations determined by a number-of-rotations switching control signal input via the number-of-rotations switching control signal line, and the fan outputs the rotational state of the fan motor via the rotational state outputting signal line, the fan including: 
        a data storage section that stores data in a non-volatile manner; and     a data output section that outputs the data stored in the data storage section via the rotational state outputting signal line.        
 
         [0014]     The fan according to the present invention retains data in the data storage section in a non-volatile manner and outputs the data via the conventionally existing rotational state outputting signal line. Therefore, the fan can provide notification of detail data about the fan without increasing the number of signal lines.  
         [0015]     In the fan according to the present invention, it is preferred that the data output section outputs data at a predetermined time when the number of rotations of the fan motor changes, for example, the data output section outputs data at a time when a power supply is turned on and the fan motor starts rotating. Alternatively, it is preferred that the data output section outputs data at a time when the fan motor decreases the number of rotations in response to a control signal that instructs the fan to decrease the number of rotations, the control signal being input via the number-of-rotations switching control signal line.  
         [0016]     Since it is ineffective to monitor the signal indicating the rotational state of the fan motor output via the rotational state outputting signal line when the fan motor is changing the number of rotations, for example, immediately after the fan motor is activated or immediately after the fan motor is instructed to change the number of rotations, a system monitors the signal when the fan motor rotates stably. Thus, if the data is output at a time when the fan motor is changing the number of rotations, there is no need to change the timing of monitoring the rotational state of the fan motor or the like, and thus, a conventional system that does not have a capability of reading data and can only monitor the rotational state of the fan motor can be applied.  
         [0017]     In addition, it is preferred that the fan according to the present invention further has a data write section that writes data transmitted via the rotational state outputting signal line to the data storage section.  
         [0018]     By providing the fan with the data write section, data the manufacturer of the fan cannot write, such as date as to when the fan is put into service, the date for an overhaul, the result of the overhaul, can be retained for later reference. Besides, data is written to the data write section via the conventionally existing rotational state outputting signal line, and therefore, there is no need to add a new signal line.  
         [0019]     For example, the data write section may write data at a time when power is being supplied and the rotation of the fan is forcibly stopped. Alternatively, the data write section may write data in response to a data write instruction signal being input via the number-of-rotations switching control signal line.  
         [0020]     As described above, the fan according to the present invention can store detail data and provide notification thereof using a conventional number of signal lines. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  shows an exemplary minimum configuration of a fan and a system that monitors and controls the fan;  
         [0022]      FIG. 2  shows a configuration of a set of data (a data packet) transmitted between the fan and a fan control section at a time according to an embodiment of the present invention;  
         [0023]      FIG. 3  shows an exemplary system configuration in which one control system controls plural fans;  
         [0024]      FIG. 4  shows signals input to or output from a motor control section of the fan shown in  FIG. 1 ;  
         [0025]      FIG. 5  shows a detail data storage section, a data/rotational state transmission circuit, and a power supply state monitoring section of the fan shown in  FIG. 1 ;  
         [0026]      FIG. 6  is a detailed block diagram showing the fan control section shown in  FIG. 1 ;  
         [0027]      FIG. 7  is a timing chart for illustrating a case where the power supply is turned on;  
         [0028]      FIG. 8  is a timing chart for illustrating a shift from high-speed rotation to low-speed rotation;  
         [0029]      FIG. 9  is a timing chart for illustrating a case where a control signal that instructs data write is transmitted from the fan control section to the fan;  
         [0030]      FIG. 10  is a timing chart for illustrating a case where the rotation of the fan is forcibly stopped; and  
         [0031]      FIG. 11  is a timing chart for illustrating a case where the fan is forcibly locked not to start rotating when the power supply is off, and then the power supply is turned on with the fan remaining locked. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     In the following, an embodiment of the present invention will be described.  
         [0033]      FIG. 1  shows a minimum configuration of a fan and a system that monitors and controls the fan.  
         [0034]      FIG. 1  shows a fan  10 , a fan control section  20 , which is a system that monitors and controls the fan  10 , a common power supply line  30  for the fan and the fan control section  20 , and a system bus  40  that connects the fan control section  20  to a host system of the fan control section  20 .  
         [0035]     The fan  10  has a detail data storage section  11 , a data/rotational state transmission circuit  12 , a power supply state monitoring section  13 , a motor control section  14  including a fan motor  141 , and a blade  15 .  
         [0036]     The detail data storage section  11  is a recordable non-volatile memory and stores detail data about the fan  10  in a non-volatile and recordable manner.  
         [0037]     The power supply state monitoring section  13  monitors the state of the power supply line  30  and transmits a PWR-ON signal to the data/rotational state transmission circuit  12  when power is supplied.  
         [0038]     The detail data stored or additionally recorded in the detail data storage section  11  include the name of the manufacturer, the fan name, the model number, the outer dimensions, the maximum air capacity, the maximum static pressure, the rated values (of the current, the voltage and the power), the steady-state number of rotations, the noise, the life time, the manufacturing factory, the lot number, the price, the type of the bearing arrangement, the frame material, the number of blades, comments about the fan&#39;s individual information, and the number-of-rotations history.  
         [0039]     When power is supplied and the fan motor  141  is rotating, the motor control section  14  transmits a FAN-PULSE signal to the data/rotational state transmission circuit  12 . The FAN-PULSE signal is a pulse string signal at a rate depending on the number of rotations of the fan motor  141  (at a rate of two pulses per rotation, in this embodiment). The blade  15  rotates by a rotational driving force of the fan motor  141 .  
         [0040]     When the fan motor  141  is not rotating although power is supplied, the motor control section  14  transmits a LOCK signal, which indicates that the fan is not rotating, to the data/rotational state transmission circuit  12 . Furthermore, if a fan&#39;s number-of-rotations switching instruction signal is input to the motor control section  14  from the fan control section  20  via a fan&#39;s number-of-rotations switching instruction line, the motor control section  14  changes the rotational speed of the fan motor in accordance with the signal and transmits a SPEED-CTL signal, which indicates the number of rotations currently designated, to the data/rotational state transmission circuit  12 .  
         [0041]     Based on the PWR-ON signal output from the power supply state monitoring section  13  and the SPEED-CTL signal, the FAN-PULSE signal and the LOCK signal output from the motor control section  14 , the data/rotational state transmission circuit  12  can determine whether to transmit the detail data stored in the detail data storage section  11  via a rotational state signal/detail data signal line, to transmit a signal indicating the rotational state of the fan motor via the rotational state signal/detail data signal line or to write detail data input via the rotational state signal/detail data signal line to the detail data storage section  11 .  
         [0042]     The data/rotational state transmission circuit  12  will be described in detail later.  
         [0043]     The rotational state signal/detail data signal line is used in a switchable manner for transmission of the FAN-PULSE signal and the like from the fan  10  to the fan control section  20  and for transmission of detail data between the fan  10  and the fan control section  20 , that is, transmission of bidirectional serial signals between the fan  10  and the fan control section  20 . In this embodiment, the start-stop-synchronized bidirectional communication (that is, the half-duplex communication) is used for the transmission of bidirectional serial signals.  
         [0044]     In addition, in this embodiment, the protocol for the bidirectional serial signals transmitted between the fan  10  and the fan control section  20  is previously specified separately.  
         [0045]      FIG. 2  shows a configuration of a set of data (a data packet) transmitted between the fan  10  and the fan control section  20  at a time according to this embodiment.  
         [0046]     As shown in  FIG. 2 , the data packet is composed of a start code (a code that identifies the beginning of data appearing when power supply to the fan is started, when a change of the number of rotations of the fan motor is instructed, and immediately after a data write request signal is transmitted), a data length, data (fan information), a check code (checksum, BCC, CRC or the like), and a stop bit.  
         [0047]     The fan control section  20  has a data communication section  21 , a rotational state determining section  22  and a fan&#39;s number-of-rotations switching instruction section  23 . The data communication section  21  receives detail data transmitted from the fan  10  via the rotational state signal/detail data signal line and, in writing detail data to the fan  10 , serves to transmit the detail data to the fan  10 . The rotational state determining section  22  receives a signal indicating the rotational state of the fan motor (that is, a FAN-PULSE signal) transmitted from the fan  10  via the rotational state signal/detail data signal line and determines the rotational state of the fan motor. The fan&#39;s number-of-rotations switching instruction section  23  transmits a fan&#39;s number-of-rotations switching instruction signal via the fan&#39;s number-of-rotations switching instruction line. Furthermore, the fan&#39;s number-of-rotations switching instruction section  23  serves also to notify the fan  10  of a detail data write timing by successively outputting a predetermined number of (three, in this example) signals for increasing or decreasing the number of rotations of the fan. Data to be written to the fan  10  is transmitted from the host system to the fan control section  20  via the system bus  40 , and then, the data communication section  21  transmits the detail data to the fan  10  via the rotational state signal/detail data signal line. On the other hand, detail data read from the detail data storage section  11  of the fan  10  and transmitted via the rotational state signal/detail data signal line is received at the data communication section  21  of the fan control section  20  and then transmitted to the host system from the fan control section  20  via the system bus  40 .  
         [0048]     The fan control section  20  will be described in detail later.  
         [0049]      FIG. 3  shows an example of system configuration in which one control system controls plural fans. Differences between this system and the system shown in  FIG. 1  will be described.  
         [0050]      FIG. 3  shows plural (two, in this example) fans  10 A and  10 B. The fans  10 A and  10 B are configured the same as the fan  10  shown in  FIG. 1 .  
         [0051]     In addition,  FIG. 3  shows a fan control section  50  that monitors and controls the plural fans  10 A and  10 B. The fan control section  50  has a core section  20 A, which corresponds to the fan control section  20  in  FIG. 1 , multiplexers  25 A and  25 B, and buffers  26 A,  26 B,  26 C and  26 D. Besides performing the same function as the fan control section  20  in  FIG. 1 , the core section  20 A outputs an MPX switching signal for switching the multiplexers  25 A and  25 B.  
         [0052]     Power supply to the two fans  10 A and  10 B is started simultaneously, and the fan&#39;s number-of-rotations switching instruction signals transmitted from the fan&#39;s number-of-rotations switching instruction section  23  arrive at the plural fans  10 A and  10 B simultaneously.  
         [0053]     On the other hand, signals indicating the states of the two fans  10 A and  10 B and detail data about the fans  10 A and  10 B are output independently from the respective fans  10 A and  10 B.  
         [0054]     Thus, the system shown in  FIG. 3  has the buffers  26 A,  26 B,  26 C and  26 D. The detail data transmitted from the two fans  10 A and  10 B are temporarily stored in the buffers  26 A and  26 C, respectively, and the core section  20 A switches the multiplexer  25 A to put the detail data from the buffers  26 A and  26 B into the data communication section  21  sequentially. Similarly, the fan-state indicating signals (FAN-PULSE signals) transmitted from the fans  10 A and  10 B are temporarily stored in the buffers  26 B and  26 D, respectively, and the core section  20 A switches the multiplexer  25 B to put the fan-state indicating signals from the buffers  26 B and  26 D into the rotational-state determining section  22  sequentially. The rotational-state determining section  22  sequentially determines the states of the fans  10 A and  10 B.  
         [0055]     When the core section  20  transmits data to the fans  10 A and  10 B, the data destined for the fans  10 A and  10 B are not transmitted directly to the fans  10 A and  10 B but transmitted to the buffers  26 A and  26 C, respectively, by switching of the multiplexer  25 A. The data are temporarily stored in the buffers  26 A and  26 C, respectively, and then transmitted from the buffers  26 A and  26 C to the fans  10 A and  10 B, respectively, at times for the fans  10 A and  10 B to receive the data.  
         [0056]     With such a configuration, one fan control section  50  can monitor and control the plural fans  10 A and  10 B.  
         [0057]     Now, referring to  FIG. 1  again, the configuration shown in  FIG. 1  will be described in detail.  
         [0058]      FIG. 4  shows signals input to or output from the motor control section  14  of the fan  10  shown in  FIG. 1 .  
         [0059]     The motor control section  14  receives a fan&#39;s number-of-rotations switching instruction signal from the fan control section  20  (see  FIG. 1 ) and transmits a SPEED-CTL signal, a LOCK signal and a FAN-PULSE signal to the data/rotational state transmission circuit  12  in the fan  10 .  
         [0060]     The motor control section  14  increases or decreases the number of rotations of the fan motor  141  in accordance with the fan&#39;s number-of-rotations switching instruction signal. The fan motor  141  is connected to the blade  15  (see  FIG. 1 ), and thus, if the fan motor  141  rotates at a high speed or low speed, the blade  15  also rotates at a high speed or low speed.  
         [0061]     When the fan motor  141  rotates normally, the motor control section  14  outputs the SPEED-CTL signal indicating whether the fan motor  141  currently rotates at the low speed or high speed and generates and outputs the FAN-PULSE signal, which is a pulse string signal containing two pulses per rotation.  
         [0062]     If the rotation of the fan motor  141  is stopped by a physical force, for example, the rotating blade is stopped by a hand of an operator, the LOCK signal that indicates that the fan motor  141  is stopped by a physical force is output.  
         [0063]      FIG. 5  shows the detail data storage section  11 , the data/rotational state transmission circuit  12 , and the power supply state monitoring section  13  of the fan  10  shown in  FIG. 1 .  FIG. 5  primarily shows details of the data/rotational state transmission circuit  12 .  
         [0064]     Referring to  FIG. 5 , the power supply state monitoring section  13  shown in  FIG. 1  is composed of a power supply voltage monitoring IC  131  and an inverter  132 . The power supply state monitoring section  13  monitors the voltage of the power supply line  30  and transmits the PWR-ON signal to a controller  121  of the data/rotational state transmission circuit  12  via the inverter  132  if a predetermined or higher voltage is input via the power supply line  30 .  
         [0065]     Referring to  FIG. 5 , the data/rotational state transmission circuit  12  shown in  FIG. 1  is composed of the controller  121 , a second timer/counter  122 , a serial/parallel converting shift register  123 , a parallel/serial converting shift register  124  and three gates  125 ,  126  and  127 .  
         [0066]     Depending on the control signals input to the gates  125 ,  126  and  127 , the gates  125 ,  126  and  127  are opened to output the input signals just as they are or closed to separate the input thereof from the output thereof.  
         [0067]     When the controller  121  of the data/rotational state transmission circuit  12  receives the PWR-ON signal from the power supply state monitoring section  13 , the controller  121  opens the gate  126  and performs a read control of the detail data storage section  11  for reading the detail data from the detail data storage section  11 . The detail data read from the detail data storage section  11  is converted into a serial signal in the parallel/serial converting shift register  124 , and the serial signal is transmitted to the rotational state signal/detail data signal line via the gate  126 . The serial signal representing the detail data is received by the data communication section  21  of the fan control section  20  shown in  FIG. 1 . At the same time as opening the gate  126 , the controller  121  sets the second timer/counter  122  for a time enough to complete the transmission of the serial signal and activates the second timer/counter  122 . When the set time has elapsed, the second timer/counter  122  transmits a count-up signal to the controller  121 . The controller  121 , upon receiving the count-up signal, closes the gate  126  and opens the gate  127 . Then, the FAN-PULSE signal transmitted from the motor control section  14  shown in  FIG. 1  is transmitted to the fan control section  20  (see  FIG. 1 ) via the gate  127  and the rotational state signal/detail data signal line.  
         [0068]     If the fan&#39;s number-of-rotations switching signal (SPEED-CTL signal) transmitted from the motor control section  14  is switched from high-speed rotation instruction to low-speed rotation instruction in a state where the PWR-ON signal is continuously input, the controller  121  opens the gate  126  and performs a read control of the detail data storage section  11  so that the data stored in the detail data storage section  11  is transmitted to the rotational state signal/detail data signal line via the gate  126 . The detail data read from the detail data storage section  11  is converted into a serial signal in the parallel/serial converting shift register  124 , and the serial signal is transmitted to the rotational state signal/detail data signal line via the gate  126  and received by the data communication section  21  of the fan control section  20  shown in  FIG. 1 . At the same time as opening the gate  126 , the controller  121  sets the second timer/counter  122  for a time enough to complete the transmission of the serial signal and activates the second timer/counter  122 . When the set time has elapsed, the second timer/counter  122  transmits a count-up signal to the controller  121 . The controller  121 , upon receiving the count-up signal, closes the gate  126  and opens the gate  127 . Then, the FAN-PULSE signal transmitted from the motor control section  14  shown in  FIG. 1  is transmitted to the fan control section  20  (see  FIG. 1 ) via the gate  127  and the rotational state signal/detail data signal line.  
         [0069]     If the fan&#39;s number-of-rotations switching signal (SPEED-CTL signal) is repeatedly switched from low-speed rotation instruction to high-speed rotation instruction plural (three, in this example) times within a predetermined time in a state where the PWR-ON signal is continuously input, the controller  121  enters a data write mode for writing data to the detail data storage section  11  and transmits a data write request signal to the rotational state signal/detail data signal line at a predetermined timing shown in the timing chart of  FIG. 9  described later. The data write request signal is transmitted as described below.  
         [0070]     The detail data storage section  11  stores not only the detail data concerning the fan but also control data, which corresponds to the data write request signal. If the SPEED-CTL signal from the fan control section  20  is switched from low-speed rotation instruction to high-speed rotation instruction a predetermined number of (three, in this example) times within a predetermined time, and it is recognized that the controller  121  is in the data write mode, the control data is read from the detail data storage section  11  at a predetermined timing shown in  FIG. 9  and converted into a serial data write request signal in the parallel/serial converting shift register  124 , and the data write request signal is transmitted to the rotational state signal/detail data signal line via the gate  126 .  
         [0071]     Once the data write request signal is transmitted in this way, the gate  126  is closed, and the gate  125  is opened.  
         [0072]     The second timer/counter  122  can perform a timer function and a counter function in parallel. When the SPEED-CTL signal is switched from low-speed rotation instruction to high-speed rotation instruction for the first time, the controller  121  sets the second timer/counter  122  for a predetermined time for determining whether the instruction switching is repeated or not, and counts the number (three, for example) of times of switching from low-speed rotation instruction to high-speed rotation instruction within the predetermined time using the second timer/counter  122 . If the count value for the predetermined time exceeds a predetermined value (three, for example), it is recognized that the controller  121  is in the data write mode.  
         [0073]     When the switching from low-speed rotation instruction to high-speed rotation instruction is repeated plural times, switching from high-speed rotation instruction to low-speed rotation instruction also occurs. Therefore, referring to the time chart described later, when the switching from high-speed rotation instruction to low-speed rotation instruction is made for the first time, a state where data is transmitted from the fan occurs. Thus, the data write is started by a write request signal transmitted after the data transmission from the fan is completed. Besides, although the fan&#39;s number-of-rotations switching signal (SPEED-CTL signal) is switched from high-speed rotation instruction to low-speed rotation instruction two more times while the fan is transmitting data, the fan does not retransmit the data.  
         [0074]     When the gate  125  is opened, and the data is transmitted to the data/rotational state transmission circuit  12  from the fan control section  20  (see  FIG. 1 ) via the rotational state signal/detail data signal line, the data, which is a serial signal, is converted into a parallel signal in the serial/parallel converting shift register  123  and written to the detail data storage section  11 . At the time of starting the data write, the controller  121  sets the second timer/counter  122  for a time enough to surely complete the data write and activates the second timer/counter  122 . When the set time has elapsed, the second timer/counter  122  generates a time-up signal. Upon receiving the time-up signal, the controller  121  closes the gate  125 , opens the gate  127  for allowing the fan control section  20  to monitor the rotational state of the fan, and transmits the FAN-PULSE signal to the rotational state signal/detail data signal line.  
         [0075]     Furthermore, the controller  121  also enters the data write mode when the controller  121  receives the LOCK signal from the motor control section  14  while it is continuously receiving the PWR-ON signal. In this case, the gate  125  is opened, and the data transmitted via the rotational state signal/detail data signal line is received at the serial/parallel converting shift register  123  through the gate  125 , converted into a parallel signal therein and written to the detail data storage section  11 . When the controller  121  receives the time-up signal indicating the completion of the data write from the second timer/counter  122 , the controller  121  closes the gate  125 , opens the gate  127 , and transmits the FAN-PULSE signal from the motor control section  14  to the rotational state signal/detail data signal line.  
         [0076]      FIG. 6  is a detailed block diagram showing the fan control section  20  shown in  FIG. 1 .  
         [0077]     Referring to  FIG. 6 , the fan control section  20  shown in  FIG. 1  is composed of an MPU  210 , an RAM  212 , a power supply voltage monitoring IC  201 , an inverter  202 , a counter  222 , and three gates  203 ,  204  and  205 . Furthermore, the MPU  210  has a memory controller  211 , a serial/parallel converting shift register  213 , a parallel/serial converting shift register  214 , a fan&#39;s number-of-rotations switching instruction section  23 , and a counter resetting section  221 . A composite of the memory controller  211 , the RAM  212 , the serial/parallel converting shift register  213  and the parallel/serial converting shift register  214  in the MPU  210  corresponds to the data communication section  21  shown in  FIG. 1 , and a composite of the counter resetting section  221  in the MPU  210 , a counter  222  separate from the MPU  210  and a determination feature in the MPU  210  corresponds to the rotational state determining section  22  shown in  FIG. 1 .  
         [0078]     The MPU  210  has a capability of determining the times to receive data from the fan, to transmit data to the fan (or write data to the fan) and to receive the FAN-PULSE signal based on the times when power supply to the fan  10  (see  FIG. 1 ) is started and when a fan&#39;s number-of-rotations switching instruction is made, transmitting/receiving data or the like at the determined times, and notifying the host system of the data received from the fan (that is, the detail data and the rotational state of the fan) via the system bus  40 . In addition, the fan control section  20  has a capability of receiving data to be written to the fan from the host system via the system bus  40 .  
         [0079]     The power supply voltage monitoring IC monitors the voltage of the power supply line  30  shared with the fan  10  (see  FIG. 1 ) and transmits the PWR-ON signal to the MPU  210  via the inverter  202  if a predetermined or higher voltage is detected.  
         [0080]     When the MPU  210  receives the PWR-ON signal, or the fan&#39;s number-of-rotations instruction transmitted from the fan&#39;s number-of-rotations switching instruction section  23  to the fan is changed from high-speed rotation instruction to low-speed rotation instruction, the MPU  210  opens the gate  203  for receiving the data from the fan.  
         [0081]     When detail data is transmitted from the fan via the rotational state signal/detail data signal line, the MPU  210  receives the detail data via the gate  203 , converts the data into parallel data in the serial/parallel converting shift register  213  and temporarily writes the parallel data to the RAM  212  under the control of the memory controller  211  that controls the access to the RAM  212 . The data temporarily written to the RAM  212  is read from the RAM  212  under the control of the memory controller  211  and transmitted to the host system (not shown) via the system bus  40 .  
         [0082]     When reception of the data from the fan  10  (see  FIG. 1 ) is completed, the gate  203  is closed, and the gate  205  is opened. A FAN-PULSE signal transmitted from the fan  10  via the rotational state signal/detail data signal line is fed to the counter  222  via the gate  205 .  
         [0083]     The counter  222  counts the pulses of the FAN-PULSE signal, and the MPU  210  periodically reads the count value from the counter  222  and checks if the count value reaches a prescribed pulse number, thereby determining whether the rotational state of the fan is adequate or not. The counter resetting section  221  resets the counter  222  each time the MPU  210  reads the count value from the counter  222 .  
         [0084]     When writing data to the fan  10 , the data received from the host system via the system bus  40  is previously stored in the RAM  212  under the control of the memory controller  211 .  
         [0085]     When the fan  10  becomes capable of receiving data from the fan control section  20 , the fan  10  transmits a data write request signal to the fan control section  20  via the rotational state signal/detail data signal line. Thus, the gate  203  is opened before the fan  10  transmits the data write request signal, and the MPU  210  receives the data write request signal via the gate  203 , converts the signal into parallel data in the serial/parallel converting shift register  213 , and determines whether the parallel data represents the write request signal or not. Data transmission from the fan control section  20  to the fan  10  is performed in two cases where data write to the fan  10  is requested from the fan&#39;s number-of-rotations switching instruction section  23  and where the blade  15  (see  FIG. 1 ) is forcibly stopped rotating. In the case where data write to the fan  10  is requested from the fan&#39;s number-of-rotations switching instruction section  23 , the MPU  210  knows the timing of the data write, and therefore, the MPU  210  closes the gate  205 , opens the gate  203  and waits. On the other hand, the MPU  210  cannot know when the blade  15  is forcibly stopped. However, since who forcibly stops the blade  15  is the operator, the operator closes the gate  205  and opens the gate  203  manually before stopping the blade  15 .  
         [0086]     Once the MPU  210  recognizes a reception of a data write request signal, the MPU  210  closes the gate  203 , opens the gate  204 , reads the data from the RAM  212  under the control of the memory controller  211 , converts the data into serial data in the parallel/serial converting shift register  214  and transmits the serial data to the fan  10  via the gate  204  and the rotational state signal/detail data signal line. Once the data transmission is completed, the gate  204  is closed, the gate  205  is opened, and the MPU  210  becomes ready to count the FAN-PULSE signals transmitted via the rotational state signal/detail data signal line using the counter  222 .  
         [0087]     According to the embodiment described herein, the fan is of a type that outputs a rotary pulse as the fan is rotating. However, if the fan is of a type that outputs a fan rotation stop signal directly indicating that the fan stops rotating, the counter  222  may be omitted.  
         [0088]      FIG. 7  is a timing chart for illustrating a case where the power supply is turned on.  FIG. 7  shows a waveform of a signal on a signal line of a conventional fan and a waveform of a signal on a signal line of the fan according to this embodiment.  
         [0089]     The relevant signal line of the fan according to this embodiment is the rotational state signal/detail data signal line shown in  FIG. 1 , and the relevant signal line of the conventional fan is a signal line corresponding to the rotational state signal/detail data signal line according to this embodiment. The same holds true for FIGS.  8  to  11  described later.  
         [0090]     The fan starts rotating when the power supply is turned on, and the number of rotations gradually increases and reaches a steady number of rotations in two or three seconds. The conventional fan continuously outputs pulse signals (FAN-PULSE signals) on the signal line depending on the number of rotations without considering data read. On the other hand, according to this embodiment, the fan transmits detail data in response to turn-on of the power supply, and after the transmission is completed, the fan is switched to transmit FAN-PULSE signals as with the conventional fan.  
         [0091]      FIG. 8  is a timing chart for illustrating a shift from high-speed rotation to low-speed rotation.  
         [0092]     When an instruction to shift from high-speed rotation to low-speed rotation is provided, the fan shifts to a steady low-speed rotation state by gradually decreasing the number of rotations in one to two seconds. The conventional fan continuously outputs the FAN-PULSE signals during the period of gradual decrease of the number of rotations onto the signal line as they are, and the signals in the period of transition are neglected. On the other hand, according to this embodiment, when an instruction to shift from high-speed rotation to low-speed rotation is provided, the fan transmits detail data onto the signal line, and after the transmission of the detail data is completed, the fan starts transmitting the rotary pulse (FAN-PULSE signal) as with the conventional fan.  
         [0093]     As described above, according to this embodiment, the period of transition in which the fan is changing the number of rotations, which has been neglected in the conventional fan, is used to transmit data from the fan.  
         [0094]      FIG. 9  is a timing chart for illustrating a case where a control signal that instructs data write is transmitted from the fan control section  20  to the fan  10 . Here, the control signal that instructs data write is composed of three successive instructions to shift from low-speed rotation to high-speed rotation.  
         [0095]     The conventional fan only outputs a pulse signal indicating that the number of rotations periodically changes according to the control signal (that is, the instructions to change the number of rotations) onto the signal line. However, according to this embodiment, the control signal is recognized as a data write instruction, and the operations described below are performed. After the first instruction to shift from low-speed rotation to high-speed rotation is provided, when the next instruction to shift from high-speed rotation to low-speed rotation is provided, a discrimination between the data write instruction and the instruction to read data from the fan  10  described above with reference to  FIG. 8  cannot be made, and the fan  10  continues to transmit the detail data onto the signal line. However, from the following change of the waveform of the control signal, the fan  10  recognizes that the control signal is a data write instruction, and transmits a data write request signal to the fan control section  20  following the transmission of the detail data. When the fan control section  20  receives the data write request, it transmits the detail data to be newly written to the fan  10  to the fan  10  via the signal line. While  FIG. 9  shows no following sequence, once the write of the detail data is completed, the fan  10  transmits a rotary pulse signal (FAN-PULSE signal) onto the signal line.  
         [0096]      FIG. 10  is a timing chart for illustrating a case where the rotation of the fan is forcibly stopped.  
         [0097]     If the rotation of the fan motor is forcibly stopped, the conventional fan simply stops transmitting the rotary pulse. However, the fan according to this embodiment transmits a data write request signal onto the signal line in response to the fan motor being forcibly stopped, and when the fan control section receives the data write request signal, the fan control section transmits detail data to be newly written to the fan  10  onto the signal line.  
         [0098]      FIG. 11  is a timing chart for illustrating a case where the fan is forcibly locked not to start rotating when the power supply is off, and then the power supply is turned on with the fan remaining locked.  
         [0099]     In response to the turn-on of the power supply, the fan first transmits detail data. Since the fan does not start rotating even after the detail data is transmitted, the controller  212  in the fan shown in  FIG. 5  continues to receive the LOCK signal, and thus, the fan transmits a data write request signal onto the signal line. The operation following the transmission of the data write request is the same as that shown in  FIG. 9  or  10 .