@pamoja/modbus

Modbus RTU requests and replies with CRC-16/MODBUS for RS485 field devices. One capability of pamoja, one memory-safe Rust core with bindings for TypeScript, Python, and C#.

Install

npm install @pamoja/modbus
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This pulls in @pamoja/native, the compiled engine. npm install pamoja is the whole framework in one package.

Example

The test that runs in CI, spliced here as it ran.

From bindings/node/guides/modbus.ts:

import { parseFrame, readHoldingRegisters, readHoldingRegistersReply } from '@pamoja/modbus'

// The device this gateway polls: a power meter at unit 17, whose manual says the three
// registers holding voltage, current and a fault word start at address 107.
const METER = 17
const FIRST_REGISTER = 107

// Ask it for those three registers. The frame is complete, checksum included, exactly as
// it goes out on the wire.
const request = readHoldingRegisters(METER, FIRST_REGISTER, 3)
console.log(`polling unit ${METER}, ${request.length} bytes out`)

// A stand-in for the meter. On a running gateway this frame arrives over RS485; here the
// library builds what a meter reporting those three values would send back.
const fromTheMeter = readHoldingRegistersReply(METER, [2301, 418, 0])

// Everything below is the gateway's own code. A reply carries its own checksum, so the
// frame is validated before any value is read out of it.
const reply = parseFrame(fromTheMeter)
const registers = reply.registers()
console.log(`voltage   ${(registers[0] / 10).toFixed(1)} V`)
console.log(`current   ${(registers[1] / 100).toFixed(2)} A`)
console.log(`faults    ${registers[2]}`)

// One flipped bit anywhere in the frame fails the checksum, which is the whole point of
// carrying one over a long RS485 run.
const mangled = Buffer.from(fromTheMeter)
mangled[2] ^= 0xff
try {
  parseFrame(mangled)
  console.log('mangled frame accepted, which should never happen')
} catch (error) {
  console.log(`mangled frame rejected: ${(error as Error).message}`)
}
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The same capability in every language

Documentation

• @pamoja/modbus reference, every class, function, and type this package exports.
• The Modbus RTU guide, with the same example in Rust, Python, and C#.
• Every capability, and the install page.

License

MIT