Abstract:
A multiprocessor system with power-on reset, comprising a plurality of printed circuit boards each provided with at least one processor, is provided. A power supply voltage monitor circuit is mounted on at least one of the printed circuit boards to provide a reset signal by detecting change of voltage when a power supply is energized. A first signal line serially connects the power supply voltage monitor circuit to all printed circuit boards, and a second signal line returning from the last printed circuit board may be provided, the processors having reset signal lines connected to the second signal line.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiprocessor system which is provided with a plurality of printed circuit boards for power-on reset of processors when the power is turned on. 
     Generally, in the case of driving a processor, the reset processing is executed for initializing programs so that each of the programs is executed correctly when the power is turned on. 
     Particularly, each processor must be reset simultaneously in the multiprocessor system which executes the one process with a plurality of processors by respectively providing the processors in an of processing function. 
     2. Description of the Prior Art 
     FIG. 1 to FIG. 3 show a structure of a multiprocessor system of the prior art. FIG. 1 is a structure providing a plurality of processors in a single printed circuit board. The printed circuit board 1 is provided with processors 2 1 , 2 2 . 
     Both processors 2 1 , 2 2  are respectively provided with a power supply voltage monitor circuit 3 to supply the power-on reset signal. Upon detection of 5V power supply voltage, the power supply voltage monitor circuit 3 outputs a reset signal. The processors 2 1 , 2 2  are reset with the power-on reset signal of the power supply voltage monitor circuit 3. 
     The structure shown in FIG. 1 has a plurality of processors on one printed circuit board. Namely, a plurality of processors operate with a common power supply. Therefore, the printed circuit board is provided with only one power supply voltage monitor circuit. This monitor circuit supplies the power-on reset signal to each processor when the power is turned ON. 
     This structure is effective for executing simple processing with the multiprocessor. However, the structure which carries out complicated processing requires many input/output circuits in the periphery of processors. Therefore, provision of many processors on one printed circuit board results in problems. 
     FIG. 2 and FIG. 3 show the structure providing the processors on a plurality of printed circuit boards. 
     In FIG. 2, 4 1  and 4 2  designate printed circuit boards and these are connected with a connector 5. 
     The processor 6 and power supply voltage monitor circuit 7 are provided on the printed circuit board 4 1 , while the processor 6 2  is provided on the printed circuit board 4 2 . 
     Here, when the power supply is turned on for the printed circuit boards 4 1  and 4 2 , the power supply voltage monitor circuit 7 detects a supply of power source voltage and outputs the reset signal. With the reset signal of the power supply voltage monitor circuit 7, the processor 6 1  is power-on reset and the processor 6 2  is also power-on reset through a connector 5. 
     As shown in FIG. 2, the structure where a plurality of processors are reset by the power supply voltage monitor circuit 7 provided on one printed circuit board has merit in that a plurality of processors are reset simultaneously. However, when power is turned on while a fault is generated in the connector connecting the printed circuit boards, only one printed circuit board is reset and the other processors are not reset. 
     As explained above, here rises a problem that the system as a whole operates without control because the other processors are not reset. 
     FIG. 3 indicates a structure that the printed circuit board 8 1  is provided with the power supply voltage monitor circuit 10 1  and the processor 9 1 . The printed circuit board 8 2  is also provided with the power supply voltage monitor circuit 10 2  and processor 9 2 . 
     In such a structure, when the power supplies of printed circuit boards 8 1  and 8 2  are turned on, the power supply voltage monitor circuit 10 1  provided on the printed circuit board 8 1  power-on resets the processor 9 1  provided on the same printed circuit board 8 1 . 
     In the same way, the power supply voltage monitor circuit 10 2  provided on the printed circuit board 8 2  power-on resets the processor 9 2  provided on the same printed circuit board 8 2 . 
     In FIG. 3, each of the power supply voltage monitor circuits outputs a reset signal at a different timing because a voltage level of each printed circuit board becomes stable at a different time. When the power is turned on, a deviation of power-on timing for all processors occurs. It is therefore no longer possible to simultaneously reset the processors 9 1  and 9 2 . 
     Therefore, the system employing the multiprocessor structure noted above results in a problem that the processor process cannot be realized stably. 
     The structure of FIG. 1 also results in a problem that the structure of the printed circuit board becomes large because a plurality of processors for different functions are accommodated on the one printed circuit board. 
     On the other hand, the structure of FIG. 2 does not result in a problem that the structure of the printed circuit board becomes large, because only one processor is provided on the one printed circuit board. 
     However, this structure results in a problem that sometimes occurs that the reset signal from the power supply voltage monitor circuit is not reset if connection between the printed circuit boards is bad in the printed circuit board that is not providing the power supply voltage monitor circuit. 
     Unlike the case where reset is not carried out as shown in FIG. 2 because connection between the printed circuit boards is not related, the structure of FIG. 3 results in a problem that if power-on timing deviates, the processors 9 1  and 9 2  are no longer reset simultaneously. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention that the processor of each printed circuit board be reset simultaneously in the multiprocessor system. Another object of the present invention is to prevent abnormal state of the multiprocessor system when connection between the printed circuit boards is defective. 
     The characteristics of the present invention are that processors are respectively provided on a plurality of printed circuit boards; a power supply voltage monitor circuit which provides a reset output signal by detecting change of voltage for power-on is provided on at least one of the printed circuit boards; the ascending signal line for cascade connecting the output of power supply voltage monitor circuit to the other printed circuit boards and the descending signal line returning from the final printed circuit board of cascade connected boards are provided and the reset signal lines of a plurality of processors are connected to the descending signal line. 
     The characteristics of other present invention include that the multiprocessor system may be provided with a power-on reset circuit which resets the processors provided on a plurality of printed circuit boards by detecting change of voltage for system power-on in the power supply voltage detecting circuit. 
     First, the processors are connected with connectors of a 2-line structure so that the processors can be reset by supplying a detected signal from the power supply voltage monitor circuit to the other printed circuit board through one line of the connector. The processors can be reset by supplying the signal for resetting the other printed circuit board to the printed circuit board through the other line of the connector. 
     Second, the microprocessor accommodating the power supply voltage monitor circuit is an active low microprocessor which is reset by a (low) L level reset signal and is constituted to output the signal sent from the power supply voltage monitor circuit to the one line of the connector through the gate circuit for waveform shaping. 
     Third, the microprocessor cascade connected by the two lines is a low active microprocessor which is reset by the L level reset signal. The power supply voltage monitor circuit, gate circuit for waveform shaping and delay circuit are provided. The power supply voltage monitor circuit and the gate circuit for waveform shaping are connected to the signal line for receiving the signal through the gate circuit for waveform shaping, while the power supply voltage monitor circuit is connected to the processor through the delay circuit and is also connected to the processor in the preceding stage through the connector and the other line. 
     Fourth, the delay circuit is formed by a monostable circuit multivibrator. 
     Fifth, the delay circuit gives a delay time for compensating for the reset period of resetting processors in synchronization. 
     Other characteristics of the present invention are as follows, in the system formed by a plurality of processors. 
     First, the processor comprises a power supply voltage monitor circuit which detects power supply voltage of the processor and outputs the reset signal for resetting the processor, and the reset signals of a plurality of power supply voltage monitor circuits are cascade-connected. When the system power supply is turned on and the predetermined voltage is detected by the power supply voltage monitor circuit, only one power supply voltage monitor circuit is reset, and the reset signal is sequentially sent to the next power supply voltage monitor circuit with the reset signal of the one power supply voltage monitor circuit and the last power supply voltage monitor circuit resets all processors. 
     Second, a 2-line connector for connecting processors is provided between the printed circuit boards, and a detected signal from the power supply voltage monitor circuit is supplied to the other printed circuit board through the one line of the connector. This reset signal is supplied, through the other one line, to the processor in the printed circuit board mounting the power supply voltage monitor circuit in order to reset such processor. 
     Third, a slave printed circuit board mounting the power supply voltage monitor circuit and one processor is connected with the master printed circuit board mounting only one processor through a 2-line connector. 
     Fourth, the slave printed circuit board is provided with a low active microprocessor which is reset by the L level reset signal and an output of the power supply voltage monitor circuit is provided to only one line of connector through the gate circuit for waveform shaping. 
     Fifth, the master printed circuit board is provided with the low active microprocessor which is reset by the L level reset signal and with the power supply voltage monitor circuit, gate circuit for waveform shaping and delay circuit, the power supply voltage monitor circuit and gate circuit for waveform shaping which are connected to the signal line received from the slave side through the gate circuit for waveform shaping. The power supply voltage monitor circuit is connected to the processor through the delay circuit and also connected to the slave side processor through the connector and the other line. 
     Sixth, the delay circuit is formed by a monostable multivibrator; and 
     Seventh, the delay circuit gives a delay time to compensate for the reset period for synchronously resetting the master side processor and slave side processor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, FIG. 2 and FIG. 3 are diagrams for explaining the prior art. 
     FIG. 4 is a diagram for explaining the first embodiment of the present invention. 
     FIG. 5 is a diagram for explaining the second embodiment of the present invention. 
     FIG. 6 is a diagram for explaining the third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be explained with reference to the accompanying drawings. 
     FIG. 4 indicates the first embodiment of the present invention. The reference numerals 30 1 , 30 2  circuit boards which respectively designate processors 31 1 , 31 2 . The numeral 32 designates a power supply voltage detecting circuit provided on the one printed circuit board 30 1  and this circuit resets the processors 31 1 , 31 2  by detecting change of voltage when the system power supply turns on. 
     The present invention is formed by connecting the processors 31 1 , 31 2  with the connector 33 accommodating two lines 33a, 33b. The detected signal from the power supply voltage monitor circuit 32 is supplied to the other printed circuit board 30 2  through the one line 33a of the connector 33 to reset the processor 31 2 . Moreover, this reset signal is supplied to the one printed circuit board 30 1  through the other line 33b of the connector 33 to reset the processor 31 1 . 
     The detected signal from the power supply voltage monitor circuit 32 is supplied to the other printed circuit board 30 2  through the one line 33a in order to reset the processor 31 2 . The reset signal from the power supply voltage monitor circuit 32 is supplied to the printed circuit board 30 1  providing the power supply voltage monitor circuit 32 through the other line 33b of the connector 33 in order to reset the processor 31 1 . 
     Namely, the processors of respective printed circuit board are simultaneously reset with the detected signal input through the connector 33. 
     Therefore, the timing is never deviated for resetting each of the processors and thus, the processors may be reset simultaneously. Moreover, if the connector provides a poor connection, all processors are not reset and thereby the system cannot be operated. 
     FIG. 5 is a second embodiment of the present invention. In this figure, 20 1  designates a slave printed circuit board and 20 2 , is a master printed circuit board. These are connected with a connector 21 comprised of two lines structure. 
     The slave printed circuit board is provided with the low active microprocessor 22 1  which is reset by the L level reset signal, a power supply voltage monitor circuit 23 1  and a gate circuit 24 for waveform shaping. 
     On the other hand, the master printed circuit board 20 2  is provided with a low active microprocessor 22 which is reset by the L level reset signal, a power supply voltage monitor circuit 23 2 , a gate circuit 24 2  for waveform shaping and a delay circuit 25 formed by monostable multivibrator. 
     The power supply voltage monitor circuit 23 1  of the printed circuit board 20 1  is connected to the gate circuit 24 2  and the power supply voltage monitor circuit 23 2  of the printed circuit board 20 2  through the line 21a of connector 21. Moreover, the power supply voltage monitor circuit 23 2  of the printed circuit board 20 2  is connected to the processor 22 2  through the delay circuit 25 and also connected to the processor 22 1  of printed circuit board 20 1  through the other line 21b of connector 21. 
     Next, operations of the second embodiment are explained. 
     If connector 21 is connected normally, when the power supply (+5V) of the slave printed circuit board 20 1  is turned on, change of voltage when the power supply is turned on is detected by the power supply voltage monitor circuit 23 1  and the detected signal is output from the terminal RST and its waveform is shaped by the gate circuit 24 1 . Thereafter, this signal is supplied to the master printed circuit board 20 2  through the line 21a of connector 21. 
     The detected signal supplied to the printed circuit board 20 2  is also waveform-shaped and is then supplied to the power supply voltage monitor circuit 23 2 . Change of voltage is detected therein and the detected signal is output from the terminal RST. 
     The detected signal output from the power supply 
     voltage monitor circuit 232 is formed as the reset signal of a predetermined pulse width by the delay circuit 25 formed by the monostable multivibrator. This signal is then supplied to the processor 22 2  to reset the processor and is also supplied to the processor 22 1  of the slave printed circuit board 20 1  through the line 21b of connector 21 in order to reset each processor. 
     Here, the delay circuit 25 provides the reset signal of the predetermined pulse width in order to reset substantially synchronously the processors 22 1  and 22 2  together when the printed circuit board 20 1  is provided comparatively far from the printed circuit board 20 2 , namely for the purpose of reset period compensation. 
     As explained previously, since the reset signal output from the delay circuit 25 is supplied in parallel to the processors 22 2  and processor 22 1 , the processors can be reset reliably like the prior art of FIG. 3. 
     Meanwhile, if the connector 21 fails to provide defective connection, both lines 21a and 21b become OFF and thereby the detected signal is never supplied to the printed circuit board 20 2  because the line 21a is OFF even when the power is turned on in the printed circuit board 20 1 . 
     Accordingly, when the connector provides defective connection, both processors 22 2  and 22 1  are never reset. 
     As a result, only one process is reset like the prior art of FIG. 2 and the system cannot operate. 
     FIG. 5 shows an example of a couple of systems, where the printed circuit board has a double-sheet structure. However the present invention is not limited thereto and may be formed in a structure where three printed circuit boards (26 1 , 26 2 , 26 3 ) are provided as shown in FIG. 6 or four sheets of printed circuit boards are used. 
     In the structure of FIG. 6, the printed circuit board 26 1  is provided with the power supply voltage monitor circuit 50 1  and processor 40 1 . 
     The printed circuit board 26 2  is provided with the power supply voltage monitor circuit 50 2  and processor 40 2 . Meanwhile, the printed circuit board 26 3  is provided with the power supply voltage monitor circuit 50 3 , processor 40 3  and delay circuit 70 1 . The printed circuit boards 26 1  and 26 2  are connected with the connector 60 1  and the printed circuit boards 26 2 , 26 3  are connected with each other by the connector 60 2 . 
     Upon detection of power voltage by printed circuit board 26 2 , the power supply voltage monitor circuit 50 1  sends the reset signal to the power supply voltage monitor circuit 50 2  through the connector 60 1 . 
     The power supply voltage monitor circuit 50 2  detects the power source voltage on of the printed circuit board 26 2  and sends the reset signal, when it is input from the power supply voltage monitor circuit 50 1 , to the power supply voltage monitor circuit 50 3 . 
     The power supply voltage monitor circuit 50 3  detects the power supply voltage of printed circuit board 26 3  and sends the reset signal to delay circuit 70, when it is input from the power supply voltage monitor circuit 50 2 , to the processors 40 1 , 40 2 , 40 3  of the printed circuit boards 26 1 , 26 2 , 26 3  through connectors 60 2  and 60 1 . 
     As explained previously, the present invention has a structure that the detected signal by power supply voltage is supplied in parallel to respective processors through the connectors without any deviation of timing. Accordingly, the respective processors may be simultaneously and reliably reset without any deviation of timing. 
     Moreover, if a connector provides a defective connection, the processors are never reset and the system is also never operated without control.