JPH07131505A - Fault detection system for serial communication circuit - Google Patents

Abstract

PURPOSE:To quickly and exactly detect whether the abnormality of communica tion is due to an error caused by the noises, etc., or the disconnection of a connection cable, etc., by providing a circuit which monitors the state of a reception data line. CONSTITUTION:A serial communication line monitoring circuit 7 is provided with two comparators CP1 and CP2 and monitors the voltage of an R X D line. In regard of the voltage of the signal line of an RS-232C, '1' is kept is a range of +3V to -12V with '0' kept in a range of +3V to +12V respectively in a normal state. Both comparators CP1 and CP2 are set so that their outputs are equal to '0' when their inputs are >+3V and <=-3V, for example, respectively. If the power supply of an external input/output equipment is cut off or a connection cable is broken, both comparators CP1 and CP2 are set at '1'. Thus the abnormality of a serial communication circuit is immediately detected by the occasional accesses given from an MPU 1. Therefore it is possible to prevent such a defective case where a process control computer carries on its control even in a communication abnormal state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to serial communication line abnormality detection for detecting an abnormality in a communication line more accurately and quickly in communication of an external device connected to an MCU.

[0002]

2. Description of the Related Art In serial communication, since data is transmitted and received at its own timing, the communication speed (baud rate) with the communication partner
Communication will not be possible if they do not match. In addition, there is work to convert parallel data to serial for communication and add start bit and stop bit.There is a framing error that occurs when the stop bit cannot be detected and data is generated when the receive buffer is full. There are many factors that cause a communication error in parallel communication, such as an overrun error that occurs when a message is received.

The main abnormalities caused by communication are an error in which a part of the data is garbled before being received due to noise or the like and normal reception is not possible, and a time-out error caused by no response from the other party even after a certain period of time. is there.

In the serial communication connected to the external input device, normally, communication is periodically performed between the external input device and the serial communication interface to refresh the data to the MCU. When an error occurs, the serial communication interface reports an error to the MCU, but the timeout error is detected by the external input device after the transmission text has been sent when the serial communication interface is the main station. That is, when the received text does not exist after a fixed time, it is first detected, and the fixed time varies depending on the external input device. On the other hand, M
The CU periodically performs calculation every fixed time, and process control including the data of the serial communication interface is executed, and there is a problem how to deal with the communication abnormality. On the other hand, in the serial communication connected to the external output device, normally, the transmission data is written from the MCU to the serial communication interface periodically, and from the transmission data, the serial communication interface creates the transmission text from the transmission data. , The control data is output from the external output device to the process by transmitting it to the external output device. Here, the serial communication interface determines whether or not the external output device normally receives the transmitted text based on the response text of the transmitted text from the external output device. When a negative response is received from the external output device at the time of abnormality, it may be due to a disturbance such as noise on the communication line or an overrun error due to the reception processing of the external output device, and the retry operation may be used for repair.
Further, the transmission operation is stopped due to a control signal (request to send) from an external output device, or there is no response after the transmission is completed. In both cases, the timer is used to monitor the timeout, and there is the same problem as the reception operation.

[0005]

External input / output device and MC
In the serial communication of the U serial communication interface, when the communication is abnormal, the communication text itself cannot be transmitted / received normally due to the disturbance or the receiving operation itself on the receiving side, and the power supply of the external input / output device. In the latter case of disconnection or disconnection of the connection cable, in the latter case, there is a problem that the detection time is required only by the time monitoring method by waiting for a response from the external input / output device. In addition, since external input / output devices other than those for process control can be easily connected just by having a serial communication function, the number of connection targets will increase, while communication procedures and control methods will also vary. Depending on the output device, there are a lot of devices that do not respond in addition to the received text that can respond, and the MCU serial communication interface cannot determine whether an abnormal text is received or no response due to non-connection, etc. There is a problem in how to deal with the MCU process.

An object of the present invention is to add a circuit for monitoring the state of a reception data line to a reception circuit of a serial communication interface section of an MCU so that the power supply status of an external input / output device and the connection status of a communication cable can be simplified. It is to make sure that it can be recognized.

[0007]

According to the present invention, a circuit for monitoring the signal status of a receiving line of a receiving unit of a serial communication interface of an MCU is provided to monitor the receiving line so that an external input / output device can perform normal communication. It is possible to detect the power supply status of the external input / output device and the disconnection of the connection cable depending on whether or not the signal is output, and detect the communication abnormality with the external input / output device in a shorter time than the time monitoring by the timeout.

[0008]

That is, in the case of the communication abnormality, the transmission status of the external input / output device and the cable connection state are monitored by monitoring the transmission line of the external input / output device without sending a transmission text and waiting for a response. Since it can be managed centrally regardless of the connected model of external I / O device, communication procedure, and communication control, the handling method of MCU process control at the time of communication error and the display to the operator through POC are unified. This leads to easier system control and maintainability.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The serial communication line abnormality detection according to the present invention will be described below with reference to FIGS. This embodiment is a system in which an MCU of a distributed control system and an external device are serially connected.

First, FIG. 1 shows a block diagram of the serial communication interface of the MCU. Serial communication interface is 1 I / O of MCU, 1: MPU,
It is composed of 2: ROM, 3: RAM, 5: communication LSI, 4: upper MCU I / F, etc., supports all communication control, and reduces the load on the MCU. In the serial communication interface, 1: MPU starts to operate according to the program in the ROM, and 5: serial communication is performed by controlling the LSI requiring communication. The input data from the external input device is temporarily stored in the RAM 3: edited, and then, together with the status of the communication result, captured by the MCU via the upper MCU I / F. Conversely, the output data to the external output device is sent from the MCU to the external output device after being stored and edited in the 3: RAM via the 4: higher MCU I / F.

7: The serial communication line abnormality detecting circuit is the most characteristic of the present invention. When a communication abnormality occurs, whether the cause is a communication error such as a parity error, an overrun error, or a framing error. It is intended to clarify that the cable is broken or the external device is powered off.

The signal line of RS232C is -3V to -12V.
Indicates "1", and +3 to + 12V indicates "0". Data is "1" or "0" when communication is normally performed.
Since the value is "1" when communication is not performed, the voltage of the signal line is always within the above range. on the other hand,
The voltage of this signal line may be near 0 V, which is outside the above range. In this case, the level is undefined, which means that the external input / output device is not connected, and the cable is disconnected or the external input / output device is powered off. By utilizing this, if the reception line is monitored, the state of the connection cable or the state of the external input / output device can be grasped.

For detecting the voltage of the receiving line, two comparators are used, and a positive voltage and a negative voltage can be detected respectively. When the RxD line has a positive voltage, the output of CP1 is ON (“0”). The detection level V + at this time is expressed by V + = R ₂ / (R ₁ + R ₂ ) × 12 (1) (1). The output of CP2 is ON (“0”) when the RxD line has a negative voltage. Detection level V at this time
- _{is, V- = R 4 / (R} 3 + R 4) × (-12) ... (2) (2) becomes equation. When the RxD line is between V- and V +, that is, when the level is indefinite, both CP1 and CP2 are OFF ("1"), and the indefinite state can be detected. It is connected to a three-state buffer after detection, and the MPU accesses this buffer to
It is possible to recognize the state of the reception line at any time.

Next, communication and its abnormality processing will be described with reference to FIGS. In this example, an example is shown in which the serial communication interface is used as a main station to periodically perform serial communication with an external input / output device. First, referring to FIG. 2, communication between 9: serial communication interface and 10: external input device will be described. In the communication operation, 9: the serial communication interface transmits a request code for requesting a text in which the data of the external input device are collected together to 10: the external input device. 10: The external input device is
9: The text is transmitted to the serial communication interface only when the request code of the serial communication interface is normally received, and a negative response is transmitted when the request code is abnormally received. On the other hand, 9: The serial communication interface starts the timer to monitor the reception time after transmitting the request code, and 10: resets the timer only when the text is normally received from the external input device to terminate normally, and otherwise A time-out error will occur.

FIG. 3 illustrates communication between 11: serial communication interface and 12: external output device. Communication operation is 11: serial communication interface is 1
2: Send a text that is a batch of output data to an external output device. 12: The external output device transmits a positive response to the serial communication interface only when the text is normally received, and transmits a negative response when the text is abnormally received. On the other hand, 11: the serial communication interface activates the timer to monitor the reception time after transmitting the text, and resets the timer to normal end only when the positive response is normally received, otherwise a time-out error occurs.

Next, the communication operation flow and its error processing will be described with reference to FIG. First, before communicating, 1
3: Perform communication line determination. This accesses the receive line monitoring register and confirms that the communication line is normal. At this time, if an abnormality occurs, immediately
21: Communication line error is set, and the communication line error is reported to the MCU. 14: The light communication transmits the request code or the output text to the external input / output device. 15: In the read communication, the input text which is the response of the request code or the positive response which is the response of the output text is received from the external input / output device. 16: If it is normal according to the normal end determination, it is determined that the communication is successful, 17: the error counter is cleared, and a series of operations is ended.
If it is abnormal, it is determined that communication has failed, and 18: error counter is incremented. Then, 19: If the number of error counts does not reach a certain count number due to the communication abnormality determination, the communication operation ends there, and communication is performed again after a period of time. At that time, if normal, the error counter is cleared. If it is abnormal, the error counter is further counted. If the error count reaches a certain count, 20: Communication error set
Report communication error to MCU.

In this way, by monitoring the communication line every time communication is performed, even if the cable is disconnected or the external input / output device is powered off, it is immediately known.

[0018]

According to the present invention, in the serial communication operation, when the communication is abnormal, the cause is a communication error, the communication cable is broken, or the external input / output device as a communication partner is cut off. It can be quickly and accurately determined. or,
Regardless of the connected model of the external input / output device, communication procedure, or communication control, it can be centrally managed, and the subsequent maintenance work can be operated efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram of a serial communication interface.

FIG. 2 is a diagram showing a communication procedure of an external input device.

FIG. 3 is a diagram showing a communication procedure of an external output device.

FIG. 4 is a flowchart of a communication operation.

[Explanation of symbols]

1 ... MPU, 2 ... ROM, 3 ... RAM, 4 ... Upper MCU
I / F, 5 ... Communication LSI, 6 ... Driver / receiver, 7 ... Communication line monitoring circuit, 8 ... MCU bus, 9 ...
Serial communication interface, 10 ... External input device,
11 ... Serial communication interface, 12 ... External output device, 13 ... Communication line determination, 14 ... Light communication, 15
... Read communication, 16 ... Normal end judgment, 17 ... Error counter clear, 18 ... Error counter increment, 19 ... Communication error judgment, 20 ... Communication error set, 21
… Communication line error set.

Claims (1)

[Claims] 1. A circuit for connecting a device to a process control computer system, and using serial communication as means for transmitting and receiving data, a circuit for monitoring a state of a reception data line in a reception circuit of a serial communication interface section of the process control computer. The serial communication line abnormality detection method characterized in that the connection status of the connected device or the connection cable can be recognized by adding.