7 865.1 Interface RS-485 RWF40... The RS-485 interface is used for integrating RWF40… controllers into data networks via MOD bus protocol. Application examples: Process visualization Plant control Reporting Master-slave principle Communication between a PC (master) and a device (slave) via MOD bus is based on the master-slave principle in the form of data query / instruction – reply. A master computer controls the exchange of data and can address up to 99 controllers via device addresses (slaves).
Transmission mode (RTU) The transmission mode used is the RTU (remote terminal unit) mode. Data are transmitted in binary format (hexadecimal) with 8 bits. The LSB (least significant bit) is transmitted first. ASCII mode is not supported. Data format The data format describes the structure of the transmitted byte. Data word 8 bit Parity bit Not Stop bit ½ bit 1 Number of bits 9 Device address The slaves’ device addresses can be selected between 1 and 99. Device address 0 is reserved.
Communication sequence Both the start and end of a data block are characterized by transmission pauses. The maximum period of time that may elapse between 2 successive characters is 3 times the period of time required for the transmission of one character. The character transmission time (period of time required for the transmission of 1 character) is dependent on the Baud rate and the type of data format.
Data query sequence Time sequence The time sequence of a data query looks as follows: Master Data query Data query Slave 7865z12e/1102 t0 t1 t2 Reply t0 t1 t0 t2 Identification of end = 3 characters (time is dependent on the Baud rate) This time is dependent on internal handling. The maximum handling time is 250 ms This is the time required by the device to switch from the transmitting mode back to the receiving mode. This time must be observed by the master before it makes a new data query.
Structure of the data blocks All data blocks use the same structure: Data structure Slave address 1 byte Function code 1 byte Data field x byte Checksum CRC16 2 bytes Every data block contains 4 fields: Slave address Device address of a certain slave Function code Function selection (reading or writing words) Data field Contains the following information: Word address Number of words Word value - Checksum Identification of transmission errors Fault handling Error codes 3 different error codes
Checksum (CRC16) The checksum (CRC16) is used to detect transmission errors. If the evaluation reveals an error, the relevant device will not respond. Calculation CRC = 0xFFF CRC = CRC XOR ByteOfMessage For (1 to 8) CRC = SHR (CRC) if (flag to the right = 1) then CRC = CRC XOR 0xA001 while (not all ByteOfMessage edited) + Example else The low byte of the checksum will be transmitted first.
Reading n words This function is used to read n words from a certain address. Data query Reply Slave address Function 0x03 or 0x04 Address of the first word 1 byte 1 byte 2 bytes Slave address Function 0x03 or 0x04 1 byte Number of bytes read 1 byte 1 byte Example Number of words (max.
Writing n words Instruction Reply Example Slave address Function 0x10 Address of first word 1 byte 1 byte 2 bytes Slave address Function 0x10 1 byte 1 byte Number of Number of words bytes (max.
Address tables Process data Address Access 0x0000 0x0002 0x0004 0x0006 Data type float float float float 0x0008 0x000A float float R/W R/W Parameter R/O R/O R/O R/W Value range Default value SPL...SPH SPL...SPH 0 0 Value range Default value 0 10 80 350 1 15 -5 3 5 0 1.
Device data Address 0x0300 0x0300 0x0306 Data type word [13] Access R/O Parameter Device data char SWVersion [11+1] char VDNNr [13+1] Value range Default value Value range Default value 0...2 * 0...1 ** 0 0 0...-1999 0...RHYS3 HYS1 HYS2 0...9999 SPL...SPH HYS3 SP1 0...1 0...1 0...1 0...1 -100...100 0...
Device state Address 0x0200 Data type word Access R/O B15 B14 B13 B12 B11 B10 B8 B9 B10 B11 B12 B13 B14 B15 0x0201 B8 Hysteresis limitation (for remote operation) Management system off (for remote operation) Self-optimization active Second setpoint active Measured value range crossing input 1 Measured value range crossing input 2 Measured value range crossing input 3 Reserved word B15 B14 B13 B12 B11 B10 B15 B14 B13 B9 Parameter Outputs and states Reserved Interface present Analog output present R
Description of operating modes General Parameter «RemoteStatus» is used to switch between the operating modes «LOCAL», «REMOTE SETPOINT» and «FULLY REMOTE». The change is always accomplished via the MOD bus. In the event the master fails or communication is lost, the RWF40... will switch to operating mode «LOCAL». The time for detecting a failure is set via the interface.
Operating mode «LOCAL» The previous functions of the RWF40... are maintained (apart from memory usage). The RWF40... can be parameterized and uploaded via the MOD bus, whereby the outputs cannot be changed. After «Power-up», the RWF40... will normally assume operating mode «LOCAL». Operating mode «REMOTE SETPOINT» The RWF40... monitors cyclic bus communication via the «Dtt» parameter (bus detection timer).
Mudulating burner Modulating controller: The management system predefines the value (degree of modulation) for the analog output via «RY». Setting the «RK2» and «RK3» by the management system has no impact. Both relays «K2» and «K3», are deenergized. Floating step controller: The management system controls the actuator («RK2» and «RK3», relays «K2» / «K3»). Setting the «RY» by the management system has no impact. In that case, the analog output delivers 0 V or 0 / 4 mA. The RWF40...
