INM 725B Rev 218913 4 6 Modbus Slave – Standard CommunicationsFunction DescriptionsThis section describes the process of reading from and writing data to a RTK 725B slaveannunciator13 4 7 Read Coil Status – Function 01 – RequestRegister AddressThis is used to address the “start” channel to be read for example the first channel in thesystem “channel 1” would be register address 00 00To read the port register coil value the port offset is used to define the start address.To read the current contact or alarm status then the start address is defined by the contactoffset.To read the input status read coils 0- 255To read the alarm status read coils 300- 555Number of RegistersThis represents the number of coils, the user wishes to read. This can be 1-255 coils.13 4 8 Read Coil Status – Function 01 – ResponseByte CountThis represents the number of bytes sentDataFor the port register this will the value stored in the address requested. With Contact statusthis represents the status of the requested coil for type of status requested.Input0 = Input Normal1 = Input AbnormalAlarm0 = Alarm Normal1 = Channel in alarmTypical Example of Message FormatTo read all of the inputs available on a 100 way annunciator with a node address of 5 using thefollowing message formatRTUADDRESS FUNCTION REGISTER ADDRESS No. of REGISTERS ERROR CHECK05 01 00 00 00 64 3C 65ASCII: ADDRESS FUNCTION REGISTERADDRESSNo. ofRegistersERRORCHECKCR LF3A 30 35 30 31 30 30 30 30 30 30 36 34 39 36 0D 0A
