RU2682435C1 - Data transmission interface - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to a data transmission method. Data transmission method is proposed therefor, which consists in the fact that between at least one leading electronic device and at least two slave electronic devices perform half-duplex data transmission. Multipoint technology of low-voltage differential signaling M-LVDS is used therefor. Messages have the form of a control packet or information packet consisting of a control packet and a data packet. Control package consists of three words, two of which include the address of the subscriber, the number of the internal address space of the requested subscriber, the initiator bit of the current transmission in the channel, the write/read operation bit, the adaptive read bit of useful information, the bit of confirmation of the reliability of the received information packet, the number of data words, and the third word determines the checksum of the other two words.EFFECT: technical result is to provide data transmission on the internal bus with a given speed, as well as to ensure the reliability of the information transmitted.1 cl, 16 dwg, 1 tbl, 1 ex

Description

The invention relates to a method for transmitting information over wire lines. This application describes a serial serial interface, namely the organization of the exchange of information between electronic devices, the characteristics of the data channel and interface devices.

The inventive interface can be used in an industrial controller with programmable logic (PLC) (hereinafter referred to as the controller), which is a computing and control unit in distributed automated process control systems (APCS). In particular, the interface described in the application is supported in the SF unit, through which data is exchanged, and which is part of the Friendship and Hornet systems on a chip (SoC), developed for use in controllers as well.

One of the problems of the controller’s developers is to provide high-speed and reliable information communication between the central processor module and the controller I / O modules, intended for inputting signals from sensors to the controller and for outputting control signals to actuators. The solution of this problem is devoted to the present invention.

When describing the proposed method and analogues used terms having the following meaning:

“Data exchange protocol” or “data transfer protocol” is a set of rules and conventions defining the content, format, time parameters, sequence and error checking in messages exchanged between devices (subscribers) of the system.

“Master” means a master device that sends data to other devices and / or requests data from other devices, i.e. is the initiator in the exchange of data with the slave device (Slave).

“Slave device” - a device that can exchange information only with the master device (Master) after the corresponding request is received from the master device.

“Subscriber” - an electronic device connected to a communication line for issuing or receiving data.

“Common bus” or “trunk” - a type of communication line in which all subscribers are connected to a common communication line. The common communication line is used by all subscribers in turn. All messages sent by individual subscribers are listened to by all other subscribers connected to the communication line, but the subscriber selects only messages addressed to him from the message flow.

“Data transmission channel” - a differential pair of wires or a differential pair of conductors on a printed circuit board, through which information is transmitted in the form of electrical signals from the sender to the receiver.

"Word" - a string of bits, considered as a single unit during their transmission, reception, switching, processing, display and storage.

“Control packet” is a data block processed by network programs as a whole. The package consists of data that plays the role of service information necessary for the implementation of the protocol.

“Information package” - a data block processed by network programs as a whole. The package consists of overhead information and useful information that must be transmitted.

The general structure of the control or information package is determined by the composition of the package and its format.

“Composition” - various data types contained in a package.

"Format" - the dimension and placement order of various types of data.

Currently, the controllers use the following serial interfaces with the organization of the MultiPoint internal bus - multi-point connection of electronic devices: CAN, FlexRay, Profibus.

Since the "new" interface was originally developed for a controller whose operation is characterized by cyclicity, mandatory polling in the cycle of all I / O modules, guaranteed reaction time (calculation of the required reaction time in the "Detailed Description of the Invention" section) and a high level of reliability of the transmitted information, then none of the "known" interfaces fully provides all the initial requirements.

The proposed method of data transfer is based on the interface described in the MIL-STD-1553В standard, dated 21 September 1978, “Department of defense interface standart for digital time division command / response multiplex data bus” (designation of the US Department of Defense standard for digital data bus with time division command / response). In our country, it was approved as GOST 26765.52-87 "Interface main serial system of electronic modules. General requirements ”, which was subsequently replaced by GOST R 52070-2003. This standard describes a centralized serial control interface used in an electronic device system and establishes requirements for the organization of information exchange, interface device functions and information transfer control, information highway characteristics and interface device characteristics. The interface operates asynchronously in command-response mode. The standard defines the composition of words - command word, data word and response word. The size of each word is 20 digits. Words begin with a clock signal (three digits), then a data field (16 bits) and end with a parity check bit. Two types of clock are defined which distinguish the control word and the response word from the data word. All information on the highway is transmitted in the Manchester-2 code. The interface described in the MIL-STD-1553B standard has the following disadvantages. So, a low information transfer rate in the channel is determined - 1 Mbit / s. The maximum message size that can be transmitted or received is no more than 32 data words. At the same time, complete control of the reliability of the transmitted information is not provided. Addressed subscribers no more than 31.

A patent search showed that the data exchange method according to the protocol described in the MIL-STD-1553B standard, which was originally developed for aircraft electronic equipment, is widely used today. The organization principles of this standard were taken as the basis for the development of new serial interfaces. Interfaces based on the MIL-STD-1553B standard with the backbone method of connecting the electronic devices of the system include: STANAG 3910, MIL-STD-1760D, MIL-STD-1773, FC-AE-1553, Space shuttle MIA bus. However, these interfaces were also developed for on-board equipment of aircraft or satellites and, therefore, completely different requirements were imposed on them than in the field of industrial automation. So, for example, in the above interfaces, data is transmitted over long distances, so an optical fiber medium is used for their transmission.

As the closest analogue to the proposed method of data transfer in an industrial controller, it is proposed to adopt the data transfer method described in US 7,243,173 B2 (patentee Rockwell Automation Technologies, US). The known method of data transmission is intended for use in the field of automation of production. The main objective of the known invention is to provide high-speed data transfer between the central processor module and peripheral devices, namely to provide a data transfer rate of at least 800 Mbaud at distances from three to forty inches. For this, a complex organization of the communication line using various devices and methods, each of which is aimed at increasing the data transfer rate, is proposed. So, it is proposed to use both parallel and serial interfaces. It is proposed that information transmitted via parallel buses from the sending side be converted to serial data and re-converted to the original form of parallel data on the receiving side. To do this, on the sending and receiving sides use series-parallel conversion circuits that convert parallel signals to serial and vice versa. For serial data transmission, LVDS technology is used to transmit data using differential signals with low voltage (TIA / EIA-644-A standard, Electrical Characteristics of Low Voltage Differential Signaling (LVDS) Interface Circuits / Note: Revision of TIA / EIA-644). The standard defines the characteristics of devices designed to support communication between one transmitter and one receiver (point-to-point) or one transmitter and several receivers (multidrop). In the known method, half-duplex data transmission is used between the conversion circuits. For this, two input and two output serial data channels are used between the conversion circuits, or four input and four output serial data channels are used for even faster data transmission. Converting signals and making circuit changes to the communication line required changes in the composition and format of the data type. The address data contains two bits that signal when a new transaction is launched or completed. The above changes, aimed at increasing the data transfer rate between the central and peripheral devices, are reflected in the claims of the known invention.

The purpose of the invention is to provide data transfer on the internal bus of the programmable logic controller with a given speed, and also to guarantee a certain level of reliability of the transmitted information.

The technical result is achieved in that the method of transmitting data in an industrial controller is that between at least one master electronic device and at least two electronic slave devices, a word-by-word data exchange is carried out, in which data is recorded from the master device to the slave device or reading data by the master from the slave. Between electronic devices, the connection between which is of the “common bus” type, half-duplex serial data transmission is carried out with a data transfer rate on one common channel in the range of 24-55 Mbit / s, for which they use multi-point technology of low-voltage differential signal transmission M-LVDS with connected to the channel transceivers of the master and slave electronic devices. Data transmission between the master electronic device and the slave electronic device is carried out in the form of a control packet or an information packet consisting of a control packet and a data packet. The control packet and the data packet consist of twenty-bit words, each of which begins with a three-bit clock signal, has sixteen information bits and ends with a parity bit. A data packet consists of one or more words of useful information and a word checksum of words of useful information. The control packet consists of three words, two of which include the subscriber's address, the number of the internal address space of the requested subscriber, the initiator bit of the current transmission in the channel, the write / read operation bit, the adaptive read bit of useful information, the validation bit of the received information packet, code the number of words in the data packet, and the third word determines the checksum of the other two words of the control packet. When reading the value of the monitored parameter, the adaptive reading bit of useful information has a different meaning in the control packet and in the information packet when the maximum possible number of words of useful information required to record the value of the controlled parameter is requested in the control packet sent by the master electronic device to the slave electronic device, and then the slave sends an information packet to the master device with fewer words of useful information than requested, and sufficient to record the current value of the monitored parameter.

Brief Description of the Drawings:

FIG. 1 is a structural diagram of the connection "common bus" of electronic devices that implement the inventive method of data exchange;

FIG. 2 is a block diagram of an M-LVDS interface with a topology of a multipoint communication line (MultiPoint);

FIG. 3 - transmission of logical zero and one in the code "Manchester-2";

FIG. 4 - clock signals of the control word and data word;

FIG. 5 - physical format of the control word;

FIG. 6 - physical format of the data word;

FIG. 7 - data packet structure (DATA);

FIG. 8 is a control packet structure (CTRL);

FIG. 9 - the structure of the information package (CTRL + DATA);

FIG. 10 - message structure "data recording in the device (Slave)";

FIG. 11 - structure of the message "broadcast message";

FIG. 12 - message structure "reading data from the device (Slave)";

FIG. 13 - the message “reading data from the device (Slave)”, in which, when measuring the current value of the parameter from the device (Slave), the maximum possible number of data words is required to write the parameter to be monitored (full read from Slave);

FIG. 14 - message “reading data from the device (Slave)”, in which from the device (Slave) the number of data words is transferred to the device (Master), sufficient to write the current value of the parameter being monitored (adaptive reading of data from Slave);

FIG. 15 and FIG. 16 is a flowchart of the operation algorithm of the device (Master) when “reading data from the device (Slave)”.

The most stringent requirement from the point of view of the controller reaction time is the time of formation of control actions in the electrical part of the steam turbine control and protection system (ЭЧСРиЗ), of which the controller is a part. The operation of the controller consists in the cyclic performance of the functions embedded in the application (technological) program. Controller response time - time from the physical change of the discrete signal at the input to the change of the physical signal at the output. The reaction time of the controller is determined by the execution time of the following phases of the controller’s duty cycle:

- the time of reading the signal in the input module (T input);

- the operating time of the I / O system on the internal bus (Bus coupler) and (Bus coupler). The input / output system integrates the internal bus and devices involved in organizing data transfer via the internal bus (interface devices);

- the execution time of the technological program (TTP);

- the time of recording the output signal in the output module (Tweak).

The reaction time of the controller is determined by the formula:

Tr = T input + T bus input + T TP + T bus output + T output

In ECHRiZ controller response time Tr should not exceed 3 ms.

The TTP technological program execution time is 1 ms.

However, it should be noted that the processes controlled by the controller occur asynchronously and a change in the value of the signal at the input can occur after reading the signal. Then the response time of the controller will be the largest due to the doubled execution time of the technological program TTP and the doubled execution time of the phases of the duty cycle (T input, T bus input, T bus output, T output):

T p = 2 × (T input + T bus input + T TP + T bus output + T output)

Therefore, the operation of the filters of the input-output modules (T input, T output) and the operation of the input / output system via the internal bus (T bus input, T bus output) takes 0.5 ms. If we take approximately that the operation of the interface devices accounts for 60% of the time 0.5 ms, then the operating time of the interface devices will be 0.3 ms.

The initial requirement for organizing a "new" interface is to provide an I / O system operating time of 0.3 ms.

Estimation of the necessary clock frequency of the "new interface":

The total number of processed physical signals in the turbine control and protection system is 500. Discrete signals (DI, DO) 60% - 300, of which DI (70%) - 210 and DO (30%) - 90. Analog signals (AI) 40 % - 200.

Discrete signals DI, DO are encoded in one bit, analog signals are encoded in 16 bits (2 bytes).

The total number of DI subscribers (based on 32 channels per module) -Ndi ~ 7; the total number of DO subscribers (based on 32 channels per module) is Ndo ~ 3; the total number of AI subscribers (based on 16 channels per module) is Nai ~ 13.

The total amount of "readable" information from sensors:

DI + AI = 210 + 200 × 16 = 3410 bits.

The total amount of "recorded" information - DO - 90 bits.

The total amount of "read / write" information is 3500 bits.

We accept the condition of serial transmission of information for 0.3 ms over the channel and determine the necessary clock frequency F:

T bit = 0.3: 3500 = 0.000086 ms. F = 1 T bit ~ 12 MHz

Protocol standards contain overhead in the form of address data, command data, error detection data, and other information. The true performance of the serial channel decreases depending on the share of overhead information in the information packet. If we assume that the amount of overhead information is approximately equal to the amount of useful information, then the clock frequency for the "new" interface should be at least 24 MHz. Therefore, assuming that the data is transmitted sequentially on one channel (one differential pair of signal conductors), the data transfer rate should be at least 24 Mbps.

To implement the data exchange method, at least one master electronic device (Master) 1 (hereinafter the device (Master) and at least two slave electronic devices (Slave) 2 (hereinafter the devices (Slave) connected to channel 4) is sufficient data transfer (Fig. 1). For example, in a controller with programmable logic, the central processor module acts as a device (Master) 1, and as a device (Slave) can be input module 2 and / or output module 3, and as a channel 4 data transfer using internal digital w Fig. 1 also shows the devices of the field (lower) level of the industrial control system, namely, the rotational speed sensor 5 connected to the input module 2 and the motor 6 connected to the output module 3. There can be two devices (Master) 1 (shown in Fig. 1), but only one of them can be active at a time.The second device (Master) 7, when it is inactive in the “monitor” mode and when the first device (Master) 1 fails, takes over the initiation of information exchange. When using the interface, a redundant channel 8 may be provided in the controller.

The development of integrated circuitry has led to the creation of fundamentally new measuring transducers - intelligent sensors (hereinafter ID), containing a converter and a microprocessor in one housing, which allows you to perform basic operations to convert, amplify and process information in the sensor itself. ID is a combination of hardware and software that provides the display of the properties of the control object in the form of some data structure generated as a result of processing the output signal of the measuring transducer according to a certain algorithm. IDs can not only control the measured values, but also carry out their assessment, correction according to certain criteria, control their own characteristics, work in a dialogue mode with the control system, receive commands, transmit measured values, usually in digital form, as well as alarm messages . The ID can provide adaptation (adaptation) to the range of changes in the values of the measured quantity, to the rate of change of the measured quantity, to the influence of influencing factors, including interference, environmental conditions, etc. As a device (Slave) 9 may be an intelligent sensor and / or intelligent electric drive. So in FIG. 1, as a device (Slave) 9, an ID is shown that is connected directly to data transmission channel 4. The interface should function asynchronously in command-response mode. The bus controller 10 controls the data transfer (Fig. 2). The bus controller can be made in the form of an integrated SF block in the SoC.

The inventive method proposes to use the M-LVDS technology of low-voltage differential signal transmission of low voltage, described in the international industrial standard TIA / EIA-899-2002 (Electrical Characteristics of Multipoint-Low-Voltage Differential Signaling (M-LVDS) Interface Circuits for Multipoint Data Interchange). Multipoint LVDS or M-LVDS is designed for multi-point bidirectional information exchange. To do this (Fig. 2) carry out half-duplex data transmission on one channel 4, which is made in the form of a differential pair of wires or conductors on a printed circuit board. To fulfill the basic requirement of multi-point design according to the M-LVDS standard, one transceiver 11 of the device (Master) interacts with the second transceiver 12 of the device (Slave). The standard allows connecting up to 32 subscribers to the bus.

Specifications of the M-LVDS standard provide high-speed signal transmission with low power consumption. The M-LVDS interface provides for hot swapping, provides stable signal integrity and a large margin of noise immunity. The maximum throughput of this interface in real conditions, depending on the application, lies in the range of 200-400 Mbit / s. The maximum distance between devices between which data is exchanged must not exceed 10 meters. Therefore, the characteristics of the M-LVDS standard provide the required method of connection between controller devices, the necessary throughput of the internal digital bus of the controller, sequential bidirectional data transfer, the necessary distance between connected devices, the ability to hot swap controller modules, and a large margin of noise immunity. All these factors made it possible to select the M-LVDS multipoint technology of low-voltage differential signaling for data transmission in the "new" interface for the controller. M-LVDS - technology provides a greater margin of noise immunity, when compared with LVDS - technology, which is more preferable for speed. In addition, M-LVDS - technology was adopted for reasons of low cost.

All information on the channel is transmitted in the Manchester-2 code. This bipolar phase-shifted code has a zero constant component, which is very important in applications with a high transmission rate. The coding of 0 and 1 is performed not by the level, but by the signal front in the middle of the clock interval (Fig. 3), which allows for bit-wise synchronization of the transmitter and receiver according to the transmitted information in a wide range of carrier frequency deviations.

Also, as in the interface according to GOST R 52070-2003, two types of clock signal are defined (Fig. 4), which allow hardware, therefore fast, to distinguish the control word from the data word and provide word-by-word synchronization of the transmitter and receiver, i.e. unambiguously determine the beginning of words in stream 0 and 1 in the channel.

In FIG. 5 shows a control word format whose size is 20 bits. The control word begins with a clock signal (3 bits), the polarity of the first half of which is positive, and the second half is negative. This is followed by 16 information bits, and the control word ends with a parity bit (P).

In FIG. 6 shows a data word format with a size of 20 bits. The data word begins with a sync signal (3 bits), the polarity of the first half of which is negative, and the second half is positive. This is followed by a 16-bit data field and the data word ends with a parity bit (P).

A word-by-word data transfer is proposed.

A data packet (DATA) (Fig. 7) consists of one or more data words and a checksum word CRC (2) data words, designed to verify the integrity of all transmitted in the data packet. Data words (useful information) - actually the data exchanged between subscribers and for the transfer of which a data packet is used.

A package that does not have data words is called a control package (CTRL). The control package can perform the function of the beginning and end of a communication session, acknowledging the receipt of an information packet, requesting an information packet. The control data is the data necessary for the subscriber to determine the fulfillment of the assigned functions and indicate his status. On Fig shows the structure of the control package (CTRL), consisting of two control words (the first word cw [0] and the second word cw [1]) and the third word cw [2] of the checksum CRC (1) of the two control words. The control words include the subscriber’s address, the internal address space of the requested subscriber, the current transfer initiator bit in the channel, the write / read operation bit, the adaptive read bit of useful information, the confirmation bit of the received information packet, the number of words in the data field.

A package that includes a control packet and a data packet is called an information packet (CTRL + DATA). In FIG. 9 shows the general structure of the information package.

Monitoring the code group of the clock signal, checking the parity check bit (P) of each word and checking the checksums of control words and data words ensure the reliability of data transmission.

Possible types of messages exchanged between the master (master) and slave (Slave) devices by sequential sequential transmission of control or information packets to each other:

- data transfer from the master device (Master) to the slave device (Slave) - "data recording in the device (Slave)" (Fig. 10);

- a broadcast message in which data from the master device (Master) is transmitted to all slave devices (Slave) - “data recording to all devices (Slave)” (Fig. 11);

- data transmission from the slave device (Slave) to the master device (Master) - "reading data from the device (Slave)" (Fig. 12).

The number of subscribers on the bus has been increased to 128. The number of internal address spaces for devices (Slave) or devices (Master) can reach 256. Internal address spaces are 1 to 256 words in size. The maximum memory size for storing messages of devices (Slave) or devices (Master) is unchanged and is 8 Kbytes. The content of the transmitted information can be any, provided it is compatible with word formats and message formats.

Data transfer between the device (Master) and devices (Slave) is divided into three phases: parameterization, configuration and data transfer. In the parameterization and configuration phase, it is checked whether the configuration and parameters of the device (Slave) correspond to the settings planned in the device (Master). It checks the type of device, the format and length of the transmitted messages, the number of inputs or outputs. In the data transfer phase, the device (Master) must implement the transfer of data to the device (Slave) and the reception of data from the device (Slave).

Consider the possible types of messages exchanged between the master and slave devices by transmitting control and information packets to each other.

The first type of message is designed to transfer data from the device (Master) to the device (Slave) - "write data to Slave" (Fig. 0). The device (Master) transmits an information packet (with the sign “record (WR)” in the control packet), and the device (Slave) receives the information packet, calculates the checksum CRC (1) of the control words and the checksum CRC (2) of the data words and compares their values with those received from the device (Master). Depending on the result of the checksum comparison, the device (Slave) either ignores the data recording task or accepts it for execution. If the information packet is received correctly, the device (Slave) sends the response control packet (CTRL) to the device (Master), in which it changes the value of the ACKN bit of validation of the received information packet. If the checksums do not match, then it is considered that the integrity of the transmitted information is violated. In this case, the device (Slave) ignores the job and sends a response control packet to the device (Master), in which the value of the ACKN bit is not changed. When transmitting data over a channel in one direction, an interval between adjacent words within a packet and between packets of not more than 100 ns is allowed. The time interval between packets following in the opposite direction shall not exceed 200 ns.

The second type of message - "broadcast message" is designed to transfer data from the device (Master) to all devices (Slave) - "write data to all Slave devices" (Fig. 1). The device (Master) transmits the information packet (with the sign “record (WR)” in the control field), and the devices (Slaves) receive the information packet, calculate the checksum CRC (1) of the control words and the checksum CRC (2) of the data words and compare their values with those received from the master device (Master). Depending on the result of the checksum comparison, the device (Slave) either ignores the data recording task or accepts it for execution. In this mode, the device (Master) after transmitting the information packet does not expect a “response packet” from the devices (Slave). When transmitting data over a channel in one direction, an interval between adjacent words within a packet and between packets of not more than 100 ns is allowed.

The third type of message is designed to transfer data from the device (Slave) to the device (Master) - "reading data from the Slave" (Fig. 2). The device (Master) transmits the control packet (with the sign “read (RD)” in the control word) and releases the channel. The addressed device (Slave) receives the control packet, calculates the CRC checksum (1) of the control words and compares its value with the value of the checksum received from the device (Master). Depending on the result of the checksum comparison, the device (Slave) either ignores the data transfer task or accepts it for execution. Upon successful comparison, the device (Slave) captures the channel and transmits a response information packet to the device (Master). The device (Master) receives a response information packet from the device (Slave) and calculates the checksum CRC (1) of the control words and the checksum CRC (2) of the data words. Upon successful comparison of the checksums, the information packet from the device (Slave) is considered accepted - the reading of data by the device (Master) from the device (Slave) is completed. When transmitting data over a channel in one direction, an interval between adjacent words within a packet and between packets of not more than 100 ns is allowed. The time interval between packets following in the opposite direction shall not exceed 200 ns.

It is known that for a data exchange method in which a device (Master) always proactively requests data from a device (Slave), it is characteristic that the device (Slave) always sends to the device (Master) the number of words of useful information that the subscriber requested from it (Master) ) in the current message. In turn, the device (Master) always (from cycle to cycle) asks for the maximum possible number of words of useful information, i.e. requests the number of words of useful information necessary to record such a value of the controlled parameter for which the maximum number of words of useful information is required. The value of the controlled parameter, measured with a given accuracy, is useful information. It is proposed to transmit on the channel only the “necessary” number of words of useful information, while traditionally in the Master / Slave systems the maximum possible number of words of useful information is transmitted. The feature of adaptive ADP reading included in the information package makes it possible, when “reading data from the device (Slave)”, to transmit on the channel only such a number of words designed to record useful information that is sufficient to record the current value of the monitored parameter, which increases the channel's performance (internal controller bus).

For example: When reading data from a device (Slave), the device (Master) requests the value of the measured (controlled) parameter, for example, the temperature value. Suppose that to transmit a temperature limit value, for example T _max = + 70 °, four data words are needed (Fig. 13). This is the maximum number of data words (useful information) required to record a controlled temperature. The device (Master) sends a control packet (CTRL) to the device (Slave) in the first word cw [0] of which SIZE = 5, ie the device (Master) requests from the device (Slave) an information packet in which the data field should consist of four data words (d [0], d [1], d [2], d [3]) and one word of the CRC checksum (2) (full read mode) (Fig. 13). But the range of nominal values of the measured temperature parameter in 90% of cases does not go beyond the values of ° С + 21 ... + 40. To record the nominal temperature values, you need one word in the data field. Therefore, each time, when transmitting the nominal temperature value, three “extra” words are sent through the channel, the bits of which are set to logical zero. Therefore, in the processor of the device (Slave), the current value of the measured temperature is analyzed, for example T ₁ = + 25 °, and set in the response information packet (CTRL + DATA) SIZE = 2, i.e. the device (Slave) sends to the device (Master) an information packet in which one data word (d [0]) and one CRC checksum word (2) (adaptive reading of data from Slave) (Fig. 14). As a result, we have a reduction in the service time ΔТр of a specific device (Slave) (I / O module, ID) by about 28%. The percentage time gain ΔТр can be calculated by the formula:

где:

Where:

x is the maximum number of data words reserved for this monitored parameter;

y is the minimum required number of words for the current value of the controlled parameter.

In order for the device (Master) not to perceive the information packet transmitted with the device (Slave) with fewer words of useful information as an error, the adaptive reading sign ADP is included in the control words of the control and information packets. In the given example, the device (Master) sends a control packet (CTRL) to the device (Slave) with the value "0" in the ADP bit and the set Size value - the number of requested words in the data packet. In turn, the device (Slave), when sending a response information packet (CTRL + DATA) with less data words than was requested in the control packet, changes the value in the ADP bit. In the response information packet, the ADP bit is set to "1". The received information packet in the control word of which ADP = 1 is perceived by the device (Master) as a command to set a new Size for receiving a data packet (DATA) from the device (Slave) (Fig. 15, Fig. 16). If the device (Slave) sends to the device (Master) as many data words as the device (Master) requested, the value of the ADP bit in the response information packet does not change and saves the value "0".

Claims (2)

1. The method of transmitting data in an industrial controller, which consists in the fact that between at least one master electronic device and at least two slave electronic devices carry out a word-by-word data exchange, in which data is written from the master to the slave or data is read by the master a device from a slave device, characterized in that between electronic devices, the connection between which is of the type "common bus", carry out half-duplex serial transmission data with a data rate of one common channel in the range of 24-55 Mbit / s, which uses multi-point technology of low-voltage differential signal transmission M-LVDS with transceivers of the master and slave electronic devices connected to the channel, data transfer between the master electronic device and the slave electronic the device is carried out in the form of a control packet or an information packet consisting of a control packet and a data packet, the control packet and the data packet consist of twenty-bit words, each of which begins with a three-bit clock signal, has sixteen information bits and ends with a parity bit, a data packet consists of one or more words of useful information and a word checksum of words of useful information, the control packet consists of three words, two of which includes the subscriber address, the internal address space number of the requested subscriber, the initiator bit of the current transmission in the channel, the write / read operation bit, the adaptive read bit of useful information, the confirmation bit the reliability of the received information packet, the code is the number of words in the data packet, and the third word determines the checksum of the other two words of the control packet, while reading the value of the controlled parameter the adaptive read bit of useful information has different meanings in the control packet and in the information packet in the case when in the control packet sent by the master electronic device to the slave electronic device the maximum possible number of words of useful information is requested, it is necessary e to record the value of the monitored parameter, and then the slave device sends to the master device an information packet with fewer words of useful information than requested and sufficient to record the current value of the monitored parameter. 2. The method of data transfer in an industrial controller according to claim 1, characterized in that the data channel is made in the form of a differential pair of wires or conductors on a printed circuit board.

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