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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 (
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Transmission mode (RTU) The transmission mode used is the RTU (remote terminal unit) mode. Data are trans- mitted 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 Parity bit Stop bit ½ bit Number of bits 8 bit Not 1 9 Device address The slaves’ device addresses can be selected between 1 and 99. Device address 0 is reserved. A maximum
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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 char- acter) is dependent on the Baud rate and the type of data format. Using a data format of 8 data bits, no parity bit and 1 stop bit, the character transmis
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Data query sequence The time sequence of a data query looks as follows: Time sequence Master Data query Data query Slave Reply t0 t1 t0 t2 7865z12e/1102 t0 Identification of end = 3 characters (time is dependent on the Baud rate) t1 This time is dependent on internal handling. The maximum handling time is 250 ms t2 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. It
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Structure of the data blocks All data blocks use the same structure: Data structure Slave address Function code Data field Checksum CRC16 1 byte 1 byte x byte 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 3 different error codes are used:
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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 else CRC = CRC XOR 0xA001 while (not all ByteOfMessage edited) The low byte of the checksum will be transmitted first. Example Data query: Reading 2 words from address 6 (CRC16 = 0x24A0) 0B 03 00 06 00 02 A0 24 CRC16 Reply: (CRC16 = 0
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Reading n words This function is used to read n words from a certain address. Data query Slave address Function 0x03 Address of the Number of Checksum or 0x04 first word words CRC16 (max. 12) 1 byte 1 byte 2 bytes 2 bytes 2 bytes Reply Slave address Function 0x03 Number of Word value(s) Checksum or 0x04 bytes read CRC16 1 byte 1 byte 1 byte x byte(s) 2 bytes Example Reading the 2 setpoints of the controller Word address = 0x0008 (setpoint SP1) Data query: 0B 03 00 08 00 04 CRC16 Reply: 0B 03 08
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Writing n words Slave Function Address Number of Number of Word Check- Instruction address 0x10 of first words bytes value(s) sum word (max. 2) CRC16 1 byte 1 byte 2 bytes 2 bytes 1 byte x byte(s) 2 bytes Reply Slave address Function 0x10 Address of Number of Checksum first word words CRC16 1 byte 1 byte 2 bytes 2 bytes 2 bytes Example Write switch-on threshold (Hys1 = -10) Word address = 0x0018 Instruction: 0B 10 00 18 00 02 04 00 00 C1 20 CRC16 Reply: 0B 10 00 18 00 02 CRC16 The high byte must
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Address tables Process data Address Data Access Parameter Value range Default type value 0x0000 float R / O Actual value E1 0x0002 float R / O Actual value E2 0x0004 float R / O Actual value E3 0x0006 float R / W Current setpoint 0x0008 float R / W SP1 First setpoint SPL...SPH 0 0x000A float R / W SP2 (=dSP) Second setpoint SPL...SPH 0 Parameter level Address Data Access Parameter Value range Default type value 0x000C float R / W AL Limit value limit comparator -1999...9999 0 0x000E float R / W
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Device data Address Data Access Parameter Value range Default type value 0x0300 word [13] R / O Device data 0x0300 char SWVersion [11+1] Software version 0x0306 char VDNNr [13+1] VdN number Remote operation Address Data Access Parameter Value range Default type value 0x0400 float R / O TEMP Actual value E3 (unfiltered) 0x0500 word R / W REM Activation remote operation 0...2 * 0 0x0501 word R / W ROFF Controller OFF in REMOTE 0...1 ** 0 SETPOINT 0x0502 float R / W RHYS1 Switch-on threshold REMOTE
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Device state Address Data type Access Parameter 0x0200 word R / O Outputs and states B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 B8 Hysteresis limitation B0 Output 1 off (for remote operation) B1 Output 3 off B9 Management system off B2 Output 2 off (for remote operation) B3 Output 4 off B10 Self-optimization active B11 Second setpoint active B12 Measured value range crossing input 1 B13 Measured value range crossing input 2 B14 Measured value range crossing input 3 B15 Reserved 0x0201
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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 oper- ating mode «LOCAL». The time for detecting a failure is set via the interface. RAM parameter for re- Remote Default after mote operation parameter «Power-up» REM Operating mode «LOCAL», «REMOTE SETPOINT
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Operating mode The previous functions of the RWF40... are maintained (apart from memory usage). «LOCAL» The RWF40... can be parameterized and uploaded via the MOD bus, whereby the out- puts cannot be changed. After «Power-up», the RWF40... will normally assume oper- ating mode «LOCAL». Operating mode The RWF40... monitors cyclic bus communication via the «Dtt» parameter (bus detec- «REMOTE SETPOINT» tion timer). Operating mode «REMOTE SETPOINT» is active as long as the bus calls within the prede
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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... always check
