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  • Publicado : 1 de noviembre de 2010
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CONTENTS: 1. PREFACE--------------------------------------------------------------------------------------------------4 2. DESCRIPTION OF THE MODBUS PROTOCOL ------------------------------------------------4 2.1. ASCII framing---------------------------------------------------------------------------------------5 2.2. RTUframing ----------------------------------------------------------------------------------------5 2.3. Characteristic of frame fields -------------------------------------------------------------------6 2.4. LRC calculation ------------------------------------------------------------------------------------7 2.5. CRC calculation------------------------------------------------------------------------------------7 2.6. Character formation during serial transmission --------------------------------------------8 2.7. Transaction interruption --------------------------------------------------------------------------8 3. FUNCTION DESCRIPTION ---------------------------------------------------------------------------8 3.1. Reading of N-registers (code 03)--------------------------------------------------------------8 3.2. Record of values into the register (code 06) ------------------------------------------------9 3.3. Record into N-registers (code 16) -------------------------------------------------------------9 3.4. Report identifying the device (code 17) ------------------------------------------------------10 4. ERROR CODES------------------------------------------------------------------------------------------10 5. REGISTER MAP OF THE N10 METER ------------------------------------------------------------12 APPENDIX A – CALCULATION OF THE CHECKSUM---------------------------------------------20


The digital programmable N10 meter destined to measure parameters of power networks has been provided with a serial interface in RS-485 standard to communicate withother devices. The asynchronous communication protocol MODBUS has been implemented on this serial interface. The configuration of serial interface parameters has been described in the Service Manual of the N10 meter. Composition of serial interface parameters concerning N10 meter: • Meter address • Transmission speed • Working modes • Information unit • Maximal response time Explanation of someabbreviations: ASCII = American Standard Code for Information Interchange RTU = LRC = CR = LF = Remote Terminal Unit Longitudinal Redundancy Check Carriage Return Line –Feed (Character) 1...32 300/600/1200/2400/4800/9600/19,000 bits/sec ASCII, RTU ASCII: 8N1, 7E1, 701 RTU: 8N2, 8E1, 801 300 ms

CRC = Cyclic Redundancy Check

MSB = Most – Significant Bit

2. DESCRIPTION OF THE MODBUS PROTOCOLThe MODBUS interface is a standard adopted by manufacturers of industrial controllers for an asynchronous character exchange of information between different devices of measuring and controlling systems. It has the following features: • Simple access rule to the interface grounded on the „master slave” principle, • Protection of transmitted messages against errors, • Confirmation of remote orderrealisation and error signalling, • Effective actions protecting against the system suspension, • Taking advantage of the asynchronous character transmission. Programmable controllers working in the MODBUS protocol can communicate with each other and with other devices using the master – slave technique, in which only one device (the master) can initiate transactions (called „queries”). The otherdevices (the slaves) respond by supplying the requested data to the master, or by taking the action requested in the query. Typical master devices include host processors and programming pannels. Typical slaves include programmable controllers. The master can address individual slaves, or can initiate a broadcast message to all slaves. Slaves return a message called a „response” to queries that...
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