Panasonic KW8M User Manual

KW8M Eco-POWER METER (1A/5ACT input type)407.4 MODBUS (RTU) Communication7.4.1 Overview of MODBUS (RTU)◆8-bit binary data in command is transmitted as it is.Data format Start bit : 1 bitData bit : 8 bits *7bits is not available.Parity : No parity, Even parity, Odd parity SelectableStop bit : 1 bit (Fixed)Error detection : CRC-16 (Cyclic Redundancy Check)Data interval : 3.5 character transmission time or more◆Message configurationRTU mode is configured to start after idle time processing of more than 3.5 character transmissionsand end after idle time processing of more than 3.5 character transmissions.3.5 idlecharactersSlaveaddressFunctioncode Data Error checkCRC-163.5 idlecharacters8-bit 8-bit ＊＊bits 16-bitMaster judges the transmission complete after no command for 4-characters idle time and process thecommand.*Transmission speed and judgment time to complete transmissionTransmission speed (bps) Judgment time to complete (ms)38400 about 1.0019200 about 2.009600 about 4.004800 about 8.002400 about 16.00◇Slave address:Slave address is an individual instrument number on the slave side and is set within the range 1 to 99(01H to 63H). Master identifies slaves by the slave address of the requested message.Slave informs master which slave is responding to master by placing its own address in the responsemessage. Slave address 0 (00H, broadcast address) can identify all slaves connected. Howeverslaves do not respond.◇Function code: Function code is command code for the slave to undertake the following action types.Function code Contents03(03H) DT Read06(06H) DT1 word write16(10H) DT several data writeFunction code is used to discern whether the response is normal (acknowledgement) or if any error(negative acknowledgement) has occurred when slave returns response message to master.When acknowledgement is returned, slave simply returns original function code. When negativeacknowledgement is returned, MSB of original function code is set as 1 for response.For example, when the master sends request message setting 00H to function code by mistake, slavereturns 80H by setting MSB to 1, because the former is an illegal function.For negative acknowledgement, the exception codes below are set to data of response message andreturned to master in order to inform it of what kind of error has occurred.Exception code Contents1(01H) Illegal Function (Non-existent function)3(03H) Illegal data value (Value out of the devise numbers)note1) Even if it commands to write (06H.10H) to non-existent data address, slave response withacknowledgement. However, it doesn’t write.note2) Even if it commands to write the value out of the setting range, slave response withacknowledgement. However, it doesn’t write.note3) The maximum number of reading slaves is 26 (57 bytes), the maximum number of writingslaves is 23 (55 bytes).