// open connection to a serial port client.connectRTUBuffered("/dev/ttyUSB0", { baudRate: 9600 }, write);

function write() { client.setID(1);

// write the values 0, 0xffff to registers starting at address 5 // on device number 1. client.writeRegisters(5, [0 , 0xffff]) .then(read); }

function read() { // read the 2 registers starting at address 5 // on device number 1. client.readHoldingRegisters(5, 2) .then(console.log); }

----
###### Read on multiple slaves

// list of meter's id const metersIdList = [10, 11, 12, 13, 14];

const getMetersValue = async (meters) => { try{ // get value of all meters for(let meter of meters) { // output value to console console.log(await getMeterValue(meter)); // wait 100ms before get another device await sleep(100); } } catch(e){ // if error, handle them here (it should not) console.log(e) } finally { // after get all data from slave, repeat it again setImmediate(() => { getMetersValue(metersIdList); }) } }

const getMeterValue = async (id) => { try { // set ID of slave await client.setID(id); // read the 1 registers starting at address 0 (first register) let val = await client.readInputRegisters(0, 1); // return the value return val.data[0]; } catch(e){ // if error return -1 return -1 } }

const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));

// start get value getMetersValue(metersIdList);

----
###### Logger Serial

// open connection to a serial port client.connectRTUBuffered("/dev/ttyUSB0", { baudRate: 9600 }); client.setID(1);

// read the values of 10 registers starting at address 0 // on device number 1. and log the values to the console. setInterval(function() { client.readHoldingRegisters(0, 10, function(err, data) { console.log(data.data); }); }, 1000);

----
###### Logger TCP

// open connection to a tcp line client.connectTCP("127.0.0.1", { port: 8502 }); client.setID(1);

// read the values of 10 registers starting at address 0 // on device number 1. and log the values to the console. setInterval(function() { client.readHoldingRegisters(0, 10, function(err, data) { console.log(data.data); }); }, 1000);

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###### Logger UDP

// open connection to a udp line client.connectUDP("127.0.0.1", { port: 8502 }); client.setID(1);

// read the values of 10 registers starting at address 0 // on device number 1. and log the values to the console. setInterval(function() { client.readHoldingRegisters(0, 10, function(err, data) { console.log(data.data); }); }, 1000);

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###### ModbusTCP Server

// set the server to answer for modbus requests console.log("ModbusTCP listening on modbus://0.0.0.0:8502"); const serverTCP = new ModbusRTU.ServerTCP(vector, { host: "0.0.0.0", port: 8502, debug: true, unitID: 1 });

serverTCP.on("socketError", function(err){ // Handle socket error if needed, can be ignored console.error(err); });

----
###### Read and Write Modbus ASCII

// open connection to a serial port client.connectAsciiSerial( "/dev/ttyUSB0", { baudRate: 9600, startOfSlaveFrameChar: 0x3A // optional: slave frame delimiter }, write);

function write() { client.setID(1);

// write the values 0, 0xffff to registers starting at address 5 // on device number 1. client.writeRegisters(5, [0 , 0xffff]) .then(read); }

function read() { // read the 2 registers starting at address 5 // on device number 1. client.readHoldingRegisters(5, 2) .then(console.log); }

----
##### "modbusdb" is an elegant wrapper over the Modbus protocol

###### Check modbusdb github repo at https://github.com/yarosdev/modbusdb for more information, feedback is welcome!
Here is an example of using modbusdb wrapper over modbus-serial:

// create an empty modbus client const client = new Modbus();

client.connectTcpRTUBuffered("127.0.0.1", { port: 8502 }, app) // or use any other available connection methods

function app() {

// First you need to define a schema for a database: // createRegisterKey(UNIT_ADDRESS, MODBUS_TABLE, REGISTER_ADDRESS, BIT_INDEX) const schema = [ { key: createRegisterKey(1, ScopeEnum.InternalRegister, 10), type: TypeEnum.Int16 }, { key: createRegisterKey(1, ScopeEnum.InternalRegister, 11), type: TypeEnum.Int32 }, { key: createRegisterKey(1, ScopeEnum.PhysicalRegister, 99), type: TypeEnum.UInt16 }, { key: createRegisterKey(1, ScopeEnum.InternalRegister, 15, 2), type: TypeEnum.Bit }, ];

// Define unit-scoped config if needed: const units = [ { address: 1, // This is unit address forceWriteMany: true, // Use 15(0x0f) and 16(0x10) functions for single register, default: false bigEndian: true, // You can use BigEndian for byte order, default: false swapWords: false, // This is applicable only for multi-registers types such as int32, float etc, default: false requestWithGaps: true, // If you are requesting addresses 10 and 13, allow to send one request to the device, default: true maxRequestSize: 32, // How many registers to be requested in one round-trip with device, default: 1 } ];

// Write values directly into modbus device as easy as possible: // NOTICE: Modbusdb under the hood will make all needed requests for you // Write operations have higher priority over the read operations db.mset([ [speedSetPoint, 60], [workingMode, 10], ]).then(result => { console.log('mset', result) }) }

Enums:

TypeEnum: (Available Data Types) 1 = Bit, 4 = Int16, 5 = UInt16, 6 = Int32, 7 = UInt32, 8 = Float

----

to get more see Examples
###### Serial connection
node-modbus-serial use node-serialport for serial communication, for serial port options settings
it passes to serial port the openOptions object,
default serial port settings are 9600,8,n,1.