modbus-connect/function-codes/write-multiple-coils.js

Modbus RTU over Web Serial and Node.js SerialPort

// function-codes/write-multiple-coils.js

const { FUNCTION_CODES } = require('../constants/constants.js');
const { allocUint8Array, uint16ToBytesBE, isUint8Array, bytesToUint16BE } = require('../utils/utils.js');

/**
 * @param {number} startAddress - адрес первой катушки
 * @param {boolean[]} values - массив значений катушек (true/false)
 * @returns {Uint8Array}
 */
function buildWriteMultipleCoilsRequest(startAddress, values) {
    if (!Array.isArray(values) || values.length < 1 || values.length > 0x07B0) {
        throw new RangeError('Values must be an array of 1 to 1968 booleans');
    }

    const byteCount = Math.ceil(values.length / 8);
    const pdu = allocUint8Array(6 + byteCount);
    pdu[0] = FUNCTION_CODES.WRITE_MULTIPLE_COILS;

    const addrBytes = uint16ToBytesBE(startAddress);
    pdu[1] = addrBytes[0];
    pdu[2] = addrBytes[1];

    const qtyBytes = uint16ToBytesBE(values.length);
    pdu[3] = qtyBytes[0];
    pdu[4] = qtyBytes[1];

    pdu[5] = byteCount;

    for (let i = 0; i < values.length; i++) {
        const byteIndex = Math.floor(i / 8);
        const bitIndex = i % 8;
        if (values[i]) {
            pdu[6 + byteIndex] |= 1 << bitIndex;
        }
    }

    return pdu;
}

/**
 * @param {Uint8Array} pdu
 * @returns {{ startAddress: number, quantity: number }}
 */
function parseWriteMultipleCoilsResponse(pdu) {
    if (!isUint8Array(pdu)) {
        throw new TypeError('PDU must be Uint8Array');
    }

    if (pdu[0] !== FUNCTION_CODES.WRITE_MULTIPLE_COILS) {
        throw new Error(`Invalid function code: expected 0x0F, got 0x${pdu[0].toString(16)}`);
    }

    const startAddress = bytesToUint16BE(pdu, 1);
    const quantity = bytesToUint16BE(pdu, 3);

    return { startAddress, quantity };
}

module.exports = {
    buildWriteMultipleCoilsRequest,
    parseWriteMultipleCoilsResponse
}