JP2003124947A - Daisy chain data input/output system by serial communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a daisy chain data input/output system for signaling at a high signaling speed between a main unit and sub-units in a comparatively simple constitution of a serial communication system. SOLUTION: The data input/output system 10 comprises a master unit 20 and a plurality of sub-units 30a, 30b connected with cables 40. A peripheral unit 50a, 50b and an output unit 60a, 60b are connected to each sub-unit 30a, 30b. It is capable of reading input data from a specified sub-unit 30 into the master unit 20 or writing output data from a specified sub-unit 30 into the output unit 60 according to an instruction from the master unit 20. It sends a signal from the master unit 20 to all the sub-units 30a, 30b, but compares address data sent from the master unit 20 with sub-unit identification data at the sub-unit 30, and executes or does not execute an instruction from the master unit 20, if both are equal or different, respectively. The data input/output system is suited to a supervisory system for equipment in factories, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a data input / output system for transmitting and receiving data between a master unit and a slave unit.

[0002]

2. Description of the Related Art As a data input / output system using a serial communication system, one master unit having a computer and a slave unit having a serial communication function are connected by a cable, and a plurality of serial communication functions are provided. There is a device in which a plurality of child devices are connected by a cable to a single parent device having a. In these data input / output systems, normally,
A signal is transmitted bidirectionally by a communication signal line between the child devices. That is, connecting the master unit and the slave unit 1
Both the signal from the master unit to the slave unit and the signal from the slave unit to the master unit are sent via the communication signal line of the book.

Further, as disclosed in Japanese Patent Application Laid-Open No. 1-238339, a plurality of interface devices (corresponding to slave units) having a gate function for serial communication are connected in series, and the interface device at the head is Those connected to one master unit equipped with a serial communication function,
As disclosed in Japanese Patent Laid-Open No. 502395, there is also a system in which a plurality of slave units are connected in a ring system and data is transmitted in a relay system. Further, in recent years, there is also a method of branching a twisted pair cable to connect one master unit and a plurality of slave units.

[0004]

However, in the conventional method, when the master unit and the slave unit are located apart from each other, the cable length for connecting the two units becomes long, so that a large amount of cables are required. Further, when a large number of cables are connected to obtain a long cable, there is a problem that a lot of wiring work is required. Further, in the conventional method, since one signal from the master unit to the slave unit and the signal from the slave unit to the master unit are transmitted by one communication signal line, the communication signal processing,
There is also a problem that the amplification circuit becomes complicated.

In the method disclosed in Japanese Patent Laid-Open No. 1-238339, the gate of the slave unit is not opened or closed without receiving the serial communication packet transmitted from the master unit and determining the gate opening / closing command. Therefore, in order to transmit the command to all the slaves, the master has to repeatedly transmit packets having the same content, which causes a problem that communication takes time.

The system disclosed in Japanese Patent Publication No. 7-502395 has a problem that the amount of data that can be communicated between the master unit and the slave unit is small. In addition, since the relay-transmitted data is partially rewritten in each child device, communication takes time.

In the method of branching the twisted pair cable to connect the master unit and the slave unit, in order to clarify the delimiter of each packet, data is transmitted between the end of transmission of a data signal and the start of transmission of the next data signal. It is necessary to provide a time during which no signal is transmitted, resulting in a problem that the communication speed becomes slow. In addition, packet start and end signals,
In order to distinguish it from the data signal, a circuit representing a value other than 0 and 1 is required, which causes a problem that the circuit becomes complicated. Further, the structure of the branching portion of the cable becomes complicated, the amount of wiring work becomes large, and bidirectional signals are transmitted by one communication signal line, so that the communication signal processing and amplification circuit becomes complicated.

[0008]

SUMMARY OF THE INVENTION According to the present invention, at least one slave having functions of receiving data input from a peripheral device, outputting data to an output device, or both, and a serial communication system. To communicate with the handset by
The above problem is solved by a data input / output system that has three master units, and the slave unit and the master unit are connected via a cable in a daisy chain system.

[0009]

Function: The master device requests the slave device having the target address to transmit the input data from the peripheral device of the slave device to the master device, or the slave device outputs the output data to the output device. Send a signal instructing to do so. If the data received from the master unit is equal to its own address, the slave unit sends the input data to the master unit according to the instruction from the master unit, or
Output required for output device. In this way, serial communication can be performed simply by connecting the master unit and the slave unit with a cable in a daisy chain system, and the amount of wiring is reduced.
The communication speed can also be increased.

[0010]

1 is a diagram showing an outline of a data input / output system of the present invention. As shown in FIG. 1, the data input / output system 10 includes a master device 20 and a slave device 30.
a, 30b (only two shown) and cables 40, 4
It is connected with 0, and each child device 30a, 30b,
Peripheral devices 50a and 50b and output devices 60a,
60b is connected.

The master device 20 transmits data input from the peripheral devices 50a and 50b to the slave devices 30a and 30b,
Alternatively, it comprises a computer C for instructing data output to the output devices 60a, 60b, a bus interface circuit B for converting the computer output into an input for a serial communication circuit, and a serial communication circuit S. The computer C is provided with a CPU having a bus of 8 bits or more, and the bus of this computer C is connected to the bus interface circuit B. The bus interface circuit B is a PLD (programmable logic device), and has the same number of input / output buses as the number of buses of the computer C to the computer C, a 6-bit slave device address bus to the serial communication circuit S, and a 12-bit output. Bus and 1
It has a 2-bit input bus. Serial communication circuit S
Is also a PLD, and is a 6-bit slave device address bus connected to the bus interface circuit B, a 12-bit output bus, a 12-bit input bus, a serial communication clock signal pin, a synchronization signal pin, and a slave device. And a pin for a master direction signal which is a signal to the master unit. When the number of buses of the computer C is sufficient, the bus interface circuit B may be omitted and the computer C may be substituted for the function.

The slave units 30a and 30b receive the data output command signal from the master unit 20 and serial communication circuits sa and sb for transmitting data to the master unit 20 by the data transmission command signal, and the serial communication circuits. Input circuits Ia and Ib for inputting data from the peripheral devices 50a and 50b and output circuits Oa and O for outputting data to the output devices 60a and 60b according to signals from the master unit received at sa and sb.
It consists of b. The serial communication circuits sa and sb are PLDs equipped with a bus interface circuit (not shown), and a 6-bit slave unit identification bus, a 12-bit output bus, a 12-bit input bus, which are connected to this bus interface circuit, A pin for a clock signal for serial communication, a pin for a synchronization signal, a pin for a child direction signal which is a signal to a slave unit, and a pin for a master direction signal which is a signal to a master unit (not shown). Have. The input circuits Ia and Ib have a 12-bit output bus (not shown) and have necessary signal lines according to the input signals. Each of the output circuits Oa and Ob has a 12-bit input bus (not shown), and has necessary signal lines according to the output signal. Depending on the specifications of the peripheral devices 50a and 50b, it may be sufficient to use only one of the input circuits Ia and Ib or the output circuits Oa and Ob. For example, when only the input circuits Ia and Ib are used, the output buses of the serial communication circuits sa and sb are unnecessary, and when only the output circuits Oa and Ob are used, the input buses of the serial communication circuits sa and sb are not necessary.

The master unit 20 and the slave unit 30a, and the slave unit 30a,
The cable 40 that connects the 30b to each other has eight signal lines, and specifically, a cable in which four twisted pair cables are combined into one cable is used. Each signal line of the twisted pair cable functions as a child-oriented signal line, a parent-oriented signal line, a clock signal line, and a synchronization signal line,
Each signal line is differentially driven to transmit and receive a signal.

FIG. 2 shows a data input / output system 1 of the present invention.
It is a figure for demonstrating the operation | movement of 0, and was shown about each signal. With reference to FIG. 2, a specific child device 30
The operation of reading the input data from to the master device 20 will be described. The computer C of the parent device connects the child device 3 to the serial communication circuit S via the bus interface circuit B.
When the address of 0 is output, the serial communication circuit S of the master device 20 outputs the output address of the slave device 30 as a serial signal from the signal line for the slave device to the "reader device" in FIG.
As shown by, the signals are transmitted in the order of a5x to a0x, and the synchronization signal is read and asserted at the timing of read synchronization. Base unit 2
The serial signal transmitted from 0 is simultaneously transmitted to the terminal slave unit via the slave unit on the way.

In the serial communication circuit s of the child device 30, the address data received by the child signal line is compared with the child device identification data. As a result of the comparison, when the address received by the child-oriented signal line and the handset identification data do not match, the handset 30 does not transmit data to the base unit 20, and when the two match, the handset 30 transmits the data input from the peripheral device 50 via the input circuit I as a serial signal from the parent-oriented signal line in the order of dbx to d0x as indicated by "reading parent" in FIG. Has been

The serial signal transmitted from the slave unit 30 is
The serial communication circuit S of the master device 20 is passed through the slave device on the way.
Will be received at. Upon receiving the read data, the serial communication circuit S of the master device 20 outputs the read request signal to the computer C, and the computer C receives the read request signal and receives the read data.
The serial communication circuit S of the master device 20 asserts the synchronization signal at the timing of read synchronization, which is the timing when the slave device 30 finishes transmitting the serial signal, and the serial communication circuit s of the slave device 30 is asserted by this assertion. It is designed to return to the initial state.

Next, the operation of writing output data from the specific slave unit 30 to the output device 60 in response to a command from the master unit 20 will be described with reference to FIG. When the computer C of the parent device 20 outputs the address of the child device 30 and the data to be output from the child device 30 to the output device 60 to the serial communication circuit S via the bus interface circuit B, the serial communication of the parent device 20 is performed. In the circuit S, the output address of the child device 30 and the data to be output from the child device 30 to the output device 60 are output as serial signals from the child signal line,
As shown in FIG. 2 for "writer", dbx to d0x,
The signals are transmitted in the order of a5x to a0x, and the synchronization signal is asserted at the write synchronization timing.

In the serial communication circuit s of the slave unit 30, the address data received by the slave-oriented signal line is compared with the slave unit identification data. As a result of the comparison, when the address data received by the child-oriented signal line and the child device identification data do not match, the child device 30 does not output the data to the output device 60, and when they match, the child device 30 Is the output device 60
To output data via the output circuit O to
Only the parity signal is transmitted from the parent-oriented signal line as a serial signal as indicated by "for writing parent" in FIG.

The parity signal transmitted from the handset 30 is
The serial communication circuit S of the master device 20 is passed through the slave device on the way.
Will be received at. Then, the serial communication circuit S of the parent device 20
When receiving the parity signal from the child device 30, outputs a parity error result to the computer C.

The serial communication circuit S of the master unit 20 is the slave unit 3
The synchronization signal is asserted at the timing of write synchronization, which is the timing when 0 has finished transmitting the parity data. By this assertion, the serial communication circuit s of the child device 30 is returned to the initial state.

The daisy chain data input / output system of the present invention described above has a suitable field of use as a monitoring system for factories and the like described below. In general, peripheral devices such as boilers and pumps are often installed in a location away from the management department of the factory, etc., and it is difficult for the management department in the factory to monitor the operation of these peripheral devices. It was In such a case, the master unit of the daisy chain data input / output system of the present invention is placed in the management department in the factory, and the peripheral equipment such as a boiler or pump is connected to the input circuit of the slave unit. The state of the peripheral device may be transmitted to the master unit through each slave unit. Note that an output device such as a siren or a light can be connected to the output circuit of each child device so that an alarm issued by a peripheral device can be notified by sound or blinking of the light.

As described above, by using the daisy chain data input / output system of the present invention, it is possible to monitor a plurality of peripheral devices at remote places at one place. In addition, the twisted pair cable that can be used to connect the parent device and the child device, and the child devices to each other is inexpensive and has an advantage that complicated wiring work is not required.

As is well known, the synchronization signal described above is not essential and can be omitted.

[0024]

As described above, according to the configuration of the present invention,
Even in serial communication, the data communication speed can be increased. In addition, the amount of wiring can be made relatively small, and there is no need to install a cable branching portion, so wiring work is simple.

Further, by transmitting a signal in one direction through a signal line and generating a synchronizing signal, a serial communication circuit including a signal amplifying function is simplified, so that a low cost system is provided. You can

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a data input / output system of the present invention.

FIG. 2 is a diagram showing an operation of each signal in the data input / output system of the present invention.

[Explanation of symbols]

10: Data input / output system 20: Base unit 30 (30a, 30b): Remote unit 40: Cable 50 (50a, 50b): peripheral device 60 (60a, 60b): output device

Claims (4)

[Claims] 1. A data input from a peripheral device is received,
It has at least one slave unit that outputs data to an output device or has both functions, and one master unit that communicates with the slave unit by a serial communication method. A data input / output system, in which devices are connected in a daisy-chain manner via a cable. 2. A serial communication system cable connecting the slave unit and the master unit, comprising a signal line from the slave unit to the master unit, a signal line from the master unit to the slave unit, and a clock signal line. The data input / output system according to claim 1, wherein three types of signal lines are provided. 3. The data input / output system according to claim 2, further comprising a serial communication type cable connecting the slave unit and the master unit with a fourth synchronization signal line for transmitting a synchronization signal only to the master unit. 4. The data input / output system according to claim 1, wherein a signal transmission direction of all signal lines is fixed to one direction as a serial communication method for connecting the slave unit and the master unit. .