support hardware automatic flow control

Author: budulinek

README.md

@@ -41,21 +41,20 @@ Screenshots of the web interface:
   - queue will accept only one requests to non-responding slaves
 
 ## How can I build it myself?
-Get the hardware. Cheap clones from China are sufficient:
+Get the hardware (cheap clones from China are sufficient) and connect together:
 
-* Arduino Nano, Uno or Mega (and possibly other)
+* Arduino Nano, Uno or Mega (and possibly other). On Mega you have to configure Serial in ADVANCED SETTINGS in the sketch.
 * W5100, W5200 or W5500 based Ethernet shield (for Nano, I recommend W5500 Ethernet Shield from RobotDyn)
-* MAX485 module
-
-Connect the hardware (on Nano and Uno, the sketch uses HW Serial, on Mega you have to configure Serial in ADVANCED SETTINGS in the sketch):
-
-* Arduino <-> MAX485
-
-* Tx1 <-> DI
-
-* Rx0 <-> RO
-
-* Pin 6 <-> DE,RE
+* TTL to RS485 module:
+  - with hardware automatic flow control (recommended)
+    Arduino <-> Module
+    Tx1 <-> Tx
+    Rx0 <-> Rx
+  - with flow controlled by pin (such as MAX485 module):
+    Arduino <-> MAX485
+    Tx1 <-> DI
+    Rx0 <-> RO
+    Pin 6 <-> DE,RE
 
 Download this repository (all *.ino files) and open arduino-modbus-rtu-tcp-gateway.ino in Arduino IDE. Download all required libraries (both are available in "library manager"). If you want, you can check the default factory settings (can be later changed via web interface) and advanced settings (can only be changed in sketch). Compile and upload your program to Arduino. Connect your Arduino to ethernet, connect your Modbus RTU slaves to MAX485 module. Use your web browser to access the web interface on default IP  http://192.168.1.254   Enjoy :-)
 

arduino-modbus-rtu-tcp-gateway/01-interfaces.ino

@@ -15,7 +15,7 @@
 
    maintainDhcp()
    - maintain DHCP lease
-   
+
    maintainUptime
    - maintains up time in case of millis() overflow
 
@@ -51,8 +51,10 @@ void startSerial() {
     charTimeout = 750;
     frameDelay = 1750;
   }
-  pinMode(rs485ControlPin, OUTPUT);
-  digitalWrite(rs485ControlPin, RS485_RECEIVE);  // Init Transceiver
+#ifdef RS485_CONTROL_PIN
+  pinMode(RS485_CONTROL_PIN, OUTPUT);
+  digitalWrite(RS485_CONTROL_PIN, RS485_RECEIVE);  // Init Transceiver
+#endif /* RS485_CONTROL_PIN */
 }
 
 void startEthernet() {

arduino-modbus-rtu-tcp-gateway/03-modbus-rtu.ino

@@ -27,13 +27,15 @@ MicroTimer txDelay;
 void sendSerial()
 {
   if (serialState == SENDING && rxNdx == 0) {        // avoid bus collision, only send when we are not receiving data
-    if (mySerial.availableForWrite() > 0 && txNdx == 0 && digitalRead(rs485ControlPin) == RS485_RECEIVE) {
-      digitalWrite(rs485ControlPin, RS485_TRANSMIT);           // Enable RS485 Transmit
+    if (mySerial.availableForWrite() > 0 && txNdx == 0) {
+#ifdef RS485_CONTROL_PIN
+      digitalWrite(RS485_CONTROL_PIN, RS485_TRANSMIT);           // Enable RS485 Transmit
+#endif /* RS485_CONTROL_PIN */
       crc = 0xFFFF;
       mySerial.write(queueHeaders.first().uid);        // send uid (address)
       calculateCRC(queueHeaders.first().uid);
     }
-    while (mySerial.availableForWrite() > 0 && txNdx < queueHeaders.first().PDUlen && digitalRead(rs485ControlPin) == RS485_TRANSMIT) {
+    while (mySerial.availableForWrite() > 0 && txNdx < queueHeaders.first().PDUlen) {
       mySerial.write(queuePDUs[txNdx]);                // send func and data
       calculateCRC(queuePDUs[txNdx]);
       txNdx++;
@@ -57,7 +59,9 @@ void sendSerial()
   } else if (serialState == DELAY && txDelay.isOver()) {
     serialTxCount += queueHeaders.first().PDUlen + 1;    // in Modbus RTU over TCP, queuePDUs already contains CRC
     if (!localConfig.enableRtuOverTcp) serialTxCount += 2;  // in Modbus TCP, add 2 bytes for CRC
-    digitalWrite(rs485ControlPin, RS485_RECEIVE);                                    // Disable RS485 Transmit
+#ifdef RS485_CONTROL_PIN
+    digitalWrite(RS485_CONTROL_PIN, RS485_RECEIVE);                                    // Disable RS485 Transmit
+#endif /* RS485_CONTROL_PIN */
     if (queueHeaders.first().uid == 0x00) {           // Modbus broadcast - we do not count attempts and delete immediatelly
       serialState = IDLE;
       deleteRequest();

arduino-modbus-rtu-tcp-gateway/arduino-modbus-rtu-tcp-gateway.ino

@@ -47,7 +47,7 @@ const int reqQueueSize = 256;        // total length of TCP or UDP requests stor
 const byte maxSlaves = 247;          // max number of Modbus slaves (Modbus supports up to 247 slaves, the rest is for reserved addresses)
 const int modbusSize = 256;          // size of a MODBUS RTU frame (determines size of serialInBuffer and tcpInBuffer)
 #define mySerial Serial              // define serial port for RS485 interface, for Arduino Mega choose from Serial1, Serial2 or Serial3         
-const byte rs485ControlPin = 6;      // Arduino Pin for RS485 Direction control
+#define RS485_CONTROL_PIN 6          // Arduino Pin for RS485 Direction control, disable if you have module with hardware flow control
 const byte ethResetPin = 7;          // Ethernet shield reset pin (deals with power on reset issue of the ethernet shield)
 const byte scanCommand[] = {0x03, 0x00, 0x00, 0x00, 0x01};  // Command sent during Modbus RTU Scan. Slave is detected if any response (even error) is received.