Modbus PDU

This is a generic module to create all the modbus PDU message types. You should then use another abstraction to TCP, RTU and ASCII.

You should not use this directly, use stream instead.

Install

npm i modbus-pdu

Examples

var Modbus = require("modbus-pdu");

// <Buffer 01 00 0d 00 14>
console.log(Modbus.ReadCoils.Request.build(13, 20));
// { address: 13, quantity: 20 }
console.log(Modbus.ReadCoils.Request.parse(new Buffer([ 0x01, 0x00, 0x0d, 0x00, 0x14 ])));

// <Buffer 94 06>
console.log(Modbus.ReadFileRecord.Exception.build(Modbus.Exception.ServerDeviceBusy));
// { code: 'ReadFileRecord', exception: 'ServerDeviceBusy' }
console.log(Modbus.Exception.parse(new Buffer([ 0x94, 0x06 ])));

// can also auto detect function code
// { code: "ReadCoils", address: 13, quantity: 20 }
console.log(Modbus.Request(new Buffer([ 0x01, 0x00, 0x0d, 0x00, 0x14 ])));
// { code: 'ReadCoils', data: [ 1, 0, 1, 1, 0, 1, 0, 1 ] }
console.log(Modbus.Response(new Buffer([ 0x01, 0x01, 0xad ])));

Function Codes

• 01 ReadCoils(address, quantity)
• 02 ReadDiscreteInputs(address, quantity)
• 03 ReadHoldingRegisters(address, quantity)
• 04 ReadInputRegisters(address, quantity)
• 05 WriteSingleCoil(address, value)
• 06 WriteSingleRegister(address, value)
• 07 ReadExceptionStatus()
• 0B GetCommEventCounter()
• 0C GetCommEventLog()
• 0F WriteMultipleCoils(address, values) // values should be Array of 1/0
• 10 WriteMultipleRegisters(address, values) // values should be Array of 2-size Buffers
• 14 ReadFileRecord(requests) // requests should be Array of objects with keys file, address and length
• 15 WriteFileRecord(requests) // requests should be Array of objects with keys file, address and values (Array of 2-size Buffers)
• 16 MaskWriteRegister(address, andmask, ormask)
• 17 ReadWriteMultipleRegisters(read_address, read_quantity, write_address, values) // values should be Array of 2-size Buffers
• 18 ReadFIFOQueue(address)
• 2B/0E ReadDeviceIdentification(code, id)

Exceptions

• 01 IllegalFunction
• 02 IllegalDataAddress
• 03 IllegalDataValue
• 04 ServerDeviceFailure
• 05 Aknowledge
• 06 ServerDeviceBusy
• 08 MemoryParityError
• 0A GatewayPathUnavailable
• 0B GatewayTargetDeviceFailedToRespond

You can create an Error object with code and message using the following code:

var err = Modbus.Exceptions.error("GatewayPathUnavailable");
console.log(err.code); // 10 (0x0A)
console.log(err.message); // "GatewayPathUnavailable"

You can use this error directly when replying to requests using the stream module.