feat: add slave functions (receiveShortFrame, sendAck, sendResponse)

src/MBusCom.cpp

@@ -227,5 +227,90 @@ uint8_t MBusCom::read_rxbuffer(uint8_t *pdata, size_t len_pdata) {
   return i; 
 }
 
+// ============================================================================
+// Slave functions
+// ============================================================================
+
+bool MBusCom::receiveShortFrame(uint8_t &cField, uint8_t &address) {
+  unsigned long start = millis();
+
+  // Wait for start byte (0x10) or ACK (0xE5)
+  while (millis() - start < 500) {
+    if (!_MbusSerial->available()) continue;
+
+    byte b = (byte)_MbusSerial->read();
+
+    // ACK received from master (unusual, ignore)
+    if (b == 0xE5) {
+      return false;
+    }
+
+    // Short frame start found
+    if (b != MBUS_FRAME_SHORT_START) continue;
+
+    // Read remaining 4 bytes: C, A, CHK, 0x16
+    byte buf[5];
+    buf[0] = b;  // 0x10
+    unsigned long byteStart = millis();
+    uint8_t idx = 1;
+    while (idx < 5 && millis() - byteStart < 200) {
+      if (_MbusSerial->available()) {
+        buf[idx++] = (byte)_MbusSerial->read();
+        byteStart = millis();
+      }
+    }
+
+    if (idx != 5) return false;
+
+    // Validate stop byte
+    if (buf[4] != MBUS_FRAME_STOP) return false;
+
+    // Validate checksum: CHK = C + A
+    if (buf[3] != (buf[1] + buf[2])) return false;
+
+    cField = buf[1];
+    address = buf[2];
+    return true;
+  }
+  return false;
+}
+
+void MBusCom::sendAck() {
+  _MbusSerial->write(0xE5);
+}
+
+void MBusCom::sendResponse(uint8_t address, const uint8_t *data, uint16_t len) {
+  // Build long frame: 0x68 | L | L | 0x68 | C | A | CI | Data... | CHK | 0x16
+  // C-field response: 0x08 (RSP_UD, no error)
+  // Address is inverted (XOR 0xFF)
+
+  uint8_t cField = 0x08;  // RSP_UD response from slave
+  uint8_t ciField = data[0];  // CI-field from data
+
+  // Frame: start(1) + len(1) + len(1) + start(1) + C(1) + A(1) + data(len) + chk(1) + stop(1)
+  // Total: 6 + len
+  uint16_t frameLen = len + 6;
+
+  // For frames > 200, length is encoded differently, but for typical
+  // M-Bus responses (< 200 bytes) single-byte length is fine.
+
+  uint8_t chk = 0;
+  chk += cField;
+  chk += address;
+  for (uint16_t i = 0; i < len; i++) {
+    chk += data[i];
+  }
+
+  _MbusSerial->write(MBUS_FRAME_LONG_START);  // 0x68
+  _MbusSerial->write((uint8_t)(len + 1));      // L = data + C + A (not including CI separately, it's part of data)
+  _MbusSerial->write((uint8_t)(len + 1));      // L repeated
+  _MbusSerial->write(MBUS_FRAME_LONG_START);  // 0x68
+  _MbusSerial->write(cField);                  // 0x08 RSP_UD
+  _MbusSerial->write(address);                 // slave address
+  _MbusSerial->write(data, len);               // CI + data records
+  _MbusSerial->write(chk);                     // checksum
+  _MbusSerial->write(MBUS_FRAME_STOP);        // 0x16
+}
+
 
 

src/MBusCom.h

@@ -59,6 +59,11 @@ class MBusCom {
   bool available();
   void application_reset(byte address);
   uint8_t read_rxbuffer(uint8_t *pdata, size_t len_pdata);// for debug use
+
+  // Slave functions
+  bool receiveShortFrame(uint8_t &cField, uint8_t &address);
+  void sendAck();
+  void sendResponse(uint8_t address, const uint8_t *data, uint16_t len);
 
 protected: