Node-RED 寫入到 Do-more PLC
要將資料從 Node-RED 寫入到 Do-more PLC，最標準且穩定的做法是讓 Node-RED 扮演 Modbus TCP 客戶端（Client），使用 modbus-write 節點，將資料寫入 Do-more 內建的 Modbus 專用暫存器（如線圈 MC 或保持暫存器 MHR）。
以下為您整理完整的設定步驟與不同資料型態（開關、16位元整數、32位元浮點數）的寫入方法。
1. 基礎節點設定 (Modbus Write)
在 Node-RED 中，拖曳 modbus-write 節點到畫布上，雙擊開啟並進行以下基礎設定：
- Server：選擇您先前建立好的 Do-more 連線（確認 IP 正確、Port 為
502）。 - Unit ID：輸入
1（或依 PLC 設定，通常預設為 1）。 - Address：輸入 0-based 的相對位址（例如欲寫入
MHR0，此處請填 0）。
2. 三種常見資料型態的寫入實作
情況 A：寫入開關/布林值（對應 Do-more 的 MC 線圈）
如果要控制 PLC 內部的某個開關接點（例如 MC0）：
modbus-write 節點設定：- FC (Function Code)：選擇
FC 5: Write Single Coil。 - Address：
0（代表 MC0）。
- 前段輸入（如
inject 節點）：- 輸出的
msg.payload 必須是布林值 true 或 false（或者是數字 1 或 0）。
情況 B：寫入 16 位元整數（對應 Do-more 的 MHR 暫存器）
如果要寫入一個 0 ~ 65535 之間的整數值（例如設定溫度、計時器目標值到 MHR0）：
modbus-write 節點設定：- FC (Function Code)：選擇
FC 6: Write Single Register。 - Address：
0（代表 MHR0）。
- 前段輸入：
- 輸出的
msg.payload 必須是一個標準整數（如 125）。
情況 C：寫入 32 位元實數/浮點數（佔用 2 個 MHR 暫存器）
當你要將一個帶有小數點的數值（如 36.5）從 Node-RED 傳入 Do-more（例如存入 MHR0 與 MHR1）時，因為 Modbus 一個暫存器只能存 16 位元，你必須先用 function 節點將浮點數拆解成兩個 16 位元整數組成的陣列，再進行寫入。
modbus-write 節點設定：- FC (Function Code)：選擇
FC 16: Write Multiple Registers ⚠️ （寫入多個暫存器必選此項）。 - Address：
0（代表從 MHR0 開始寫）。 - Quantity：
2（代表連續寫入 2 個暫存器）。
- 前段接一個
function 節點，寫入以下轉換程式碼：
// 假設要寫入的浮點數值來自 msg.payload (例如 36.5)
let floatValue = Number(msg.payload);
// 建立一個 4 內容值的 Buffer 區塊 (32 bits)
const buf = Buffer.alloc(4);
// 將浮點數以 Big-Endian 格式寫入 Buffer
buf.writeFloatBE(floatValue, 0);
// 將 4 個 Bytes 拆解組合成 2 個 16 位元的無正負號整數 (UInt16)
let word1 = buf.readUInt16BE(0); // 高位字組 (High Word)
let word2 = buf.readUInt16BE(2); // 低位字組 (Low Word)
// 將準備好的陣列賦值給 msg.payload 輸出給 modbus-write 節點
msg.payload = [word1, word2];
return msg;
- 。
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Do-more 轉 Modbus 記憶體對應表
在 Node-RED 的 Modbus 節點設定中，Address（位址） 通常採用 0 起始（0-based） 的相對位址（即協定內定址）。
| Do-more 記憶體類型 | 說明 | Modbus 類型 / 功能碼 (FC) | Node-RED 位址 (0-based) | 備註 / 對應範例 |
|---|
MC0 – MC1023 | Modbus 專用線圈 | Coils (FC1 / FC5 / FC15) | 0 – 1023 | MC0 ＝ 位址 0 |
MI0 – MI1023 | Modbus 專用輸入接點 | Discrete Inputs (FC2) | 0 – 1023 | MI0 ＝ 位址 0 |
MHR0 – MHR2047 | Modbus 專用保持暫存器 | Holding Registers (FC3/FC4/FC6/FC16) | 0 – 2047 | MHR0 ＝ 位址 0 |
MIR0 – MIR2047 | Modbus 專用輸入暫存器 | Input Registers (FC4) | 0 – 2047 | MIR0 ＝ 位址 0 |
