modbus-connect/src/function-codes/read-input-registers.ts

Modbus RTU over Web Serial and Node.js SerialPort

// src/function-codes/read-input-registers.ts

import { ReadInputRegistersResponse } from '../types/modbus-types.js';

const FUNCTION_CODE = 0x04;
const MIN_QUANTITY = 1;
const MAX_QUANTITY = 125;
const REQUEST_SIZE = 5; // 1 (FC) + 2 (Addr) + 2 (Qty)
const RESPONSE_HEADER_SIZE = 2; // FC (1) + ByteCount (1)
const UINT16_SIZE = 2;

/**
 * Строит PDU-запрос для чтения input-регистров (FC 0x04)
 * @param startAddress - начальный адрес (0x0000–0xFFFF)
 * @param quantity - количество регистров (1–125)
 * @returns Uint8Array
 */
export function buildReadInputRegistersRequest(startAddress: number, quantity: number): Uint8Array {
  if ((quantity | 0) !== quantity || quantity < MIN_QUANTITY || quantity > MAX_QUANTITY) {
    throw new RangeError(`Quantity must be integer ${MIN_QUANTITY}-${MAX_QUANTITY}`);
  }

  const buffer = new Uint8Array(REQUEST_SIZE);
  buffer[0] = FUNCTION_CODE;
  buffer[1] = startAddress >>> 8; // Старший байт адреса
  buffer[2] = startAddress & 0xff; // Младший байт адреса
  buffer[3] = quantity >>> 8; // Старший байт кол-ва
  buffer[4] = quantity & 0xff; // Младший байт кол-ва

  return buffer;
}

/**
 * Разбирает PDU-ответ с input-регистрами (FC 0x04)
 * @param pdu - принятый PDU-пакет
 * @returns number[] - массив значений регистров
 * @throws TypeError|Error - при неверных данных
 */
export function parseReadInputRegistersResponse(pdu: Uint8Array): ReadInputRegistersResponse {
  if (!(pdu instanceof Uint8Array)) {
    throw new TypeError('PDU must be Uint8Array');
  }

  const pduLength = pdu.length;
  if (pduLength < RESPONSE_HEADER_SIZE) {
    throw new Error('PDU too short');
  }

  if (pdu[0] !== FUNCTION_CODE) {
    throw new Error(
      `Invalid function code: expected 0x04, got 0x${pdu[0]?.toString(16).padStart(2, '0')}`
    );
  }

  const byteCount = pdu[1]!;
  if (byteCount % UINT16_SIZE !== 0) {
    throw new Error(`Invalid byte count: must be multiple of ${UINT16_SIZE}`);
  }

  const expectedLength = RESPONSE_HEADER_SIZE + byteCount;
  if (pduLength !== expectedLength) {
    throw new Error(`Invalid PDU length: expected ${expectedLength}, got ${pduLength}`);
  }

  if (byteCount === 0) {
    return [];
  }

  const buffer = pdu.buffer || pdu;
  const byteOffset = (pdu.byteOffset || 0) + RESPONSE_HEADER_SIZE;
  const registerCount = byteCount / UINT16_SIZE;

  if (byteOffset % UINT16_SIZE === 0) {
    const uint16View = new Uint16Array(buffer, byteOffset, registerCount);
    return Array.from(uint16View);
  } else {
    const registers: number[] = new Array(registerCount);
    const view = new DataView(buffer, byteOffset, byteCount);
    for (let i = 0; i < registerCount; i++) {
      registers[i] = view.getUint16(i * UINT16_SIZE, false);
    }
    return registers;
  }
}