ESP8266 Crash when RS485 is disconnected from MAX485

[luisgcu]

ModbusMaster version

[2.0.1]

Arduino IDE version

[1.8.2]

Arduino Hardware

[ESP8266, NodeMCU1.0 ESP-12E]

Platform Details

[Operating system distribution and release version]

---

Scenario:

[Read holding register (10) from a VFD, Max485 is conected to GPIO, 14,12 on the ESP8266 using the software serial]

Steps to Reproduce:

[II am able to read modbus registers without problem , the only problem that I have is, if I disconnect the RS485 conection from the MAX485 then the ESP8266 crash and reset over and over again]

THE CODE

include

include

/! We're using a MAX485-compatible RS485 Transceiver. Rx/Tx is hooked up to the hardware serial port at 'Serial'. The Data Enable and Receiver Enable pins are hooked up as follows: /

define MAX485_DE 5 // was 5(moteino) //and was 2(d4) on esp8266 but have trouble

define MAX485_RE_NEG 4 // was 6

define NANO_HSP(m,n) (m *100+ n-1) ///<

ModbusMaster node;

SoftwareSerial mySerial(14, 12, false,256); //esp8266 void preTransmission() { digitalWrite(MAX485_RE_NEG, 1); digitalWrite(MAX485_DE, 1); }

void postTransmission() { digitalWrite(MAX485_RE_NEG, 0); digitalWrite(MAX485_DE, 0); }

void setup() { pinMode(MAX485_RE_NEG, OUTPUT); pinMode(MAX485_DE, OUTPUT);

// Init in receive mode digitalWrite(MAX485_RE_NEG, 0); digitalWrite(MAX485_DE, 0); Serial.begin(19200); // Commander SK @ 19200 mySerial.begin(19200); Serial.println("Modbus-Master");

// Modbus slave ID 1 node.begin(1, mySerial); // Callbacks allow us to configure the RS485 transceiver correctly node.preTransmission(preTransmission); node.postTransmission(postTransmission); }

bool state = true;

void loop() { uint8_t result;

result=node.readHoldingRegisters(NANO_HSP(18,11), 10); //

if (result == node.ku8MBSuccess) { Serial.println("Data: "); // Serial.println(node.getResponseBuffer(1)); for (uint8_t j = 0; j < 10; j++) Serial.println(node.getResponseBuffer(j),DEC);

              mySerial.flush();
             // node.clearTransmitBuffer();

} else { Serial.println("NO- RESPONSE"); //mySerial.flush(); }

delay(3000); Serial.println("running..."); }

#############

THE Crash from the ESP8266

Soft WDT reset

ctx: cont sp: 3ffef4f0 end: 3ffef820 offset: 01b0

stack>>> 3ffef6a0: feefeffe feefeffe feefeffe 00000008
3ffef6b0: 00000008 00000003 3ffee4f4 402020ba
3ffef6c0: 12070301 bc640a00 006f0000 014d01de
3ffef6d0: 7f0080bc c03930ff feefefda feefeffe
3ffef6e0: feefeffe feefeffe feefeffe feefeffe
3ffef6f0: feefeffe feefeffe feefeffe feefeffe
3ffef700: feefeffe feefeffe feefeffe feefeffe
3ffef710: feefeffe feefeffe feefeffe feefeffe
3ffef720: feefeffe 00000004 3ffef78f 40202e18
3ffef730: feefeffe feefeffe feefeffe 3ffee73c
3ffef740: 00000031 0000000a 3ffee73c 40202721
3ffef750: 3ffef78b feefeffe feefeffe feefeffe
3ffef760: feefeffe feefeffe 3ffef78a 402027d5
3ffef770: feefeffe feefeffe feefeffe 00004b00
3ffef780: 0000001c 00000000 31fee73c 35343332
3ffef790: feefef00 00000001 3ffe8669 40202e18
3ffef7a0: 00000009 00000009 3ffe8459 3ffee7f0
3ffef7b0: 3ffee4f4 0000000a 3ffee73c 40202721
3ffef7c0: 0000381a 000000e2 3ffee73c 40202721
3ffef7d0: 3ffe8450 3ffee7f0 3ffee73c 3ffee7f0
3ffef7e0: 3ffee4f4 00000000 3ffee4f4 40202260
3ffef7f0: 00000000 00000000 00000001 40201d38
3ffef800: 3fffdad0 00000000 3ffee7e8 40202ba4
3ffef810: feefeffe feefeffe 3ffee800 40100708
<<<stack<<<

##############################

thanks for any guidance.

[sathiyakumar3]

I too have a similar problem, the esp8266 getting soft reset every time when the modbus device goes offline.

[icandura]

I got same problem, too. But the chip what I use is SP3485 rather than MAX3485.

[icandura]

I think I found one of the reasons for this problem. When my MODBUS_MASTER is working under the software serial port, it resets by WDT when the slave disconnects. But when my MODBUS master works on the hardware serial port, it works normally no matter the slave is disconnected or not. So I think the problem lies in the software serial port.

[TLS1000]

Hi, i'm having the exact same problem. I'm using MAX3485 with level shifting. Did someone find a solution?

[TLS1000]

hi, I went a little deeper on the working of the software wathdog of the ESP8266. Problem is the waiting on a response from a modbus slave (espacially during testing with no slave connected), during that time the software wathdog fires because it thinks the program hangs.

you can solve it elegantly by disabling the watchdog during modbus reads: ESP.wdtDisable(); result = node.readHoldingRegisters(15206,3); ESP.wdtEnable(1);

I have no more soft WDT resets anymore

[Warlib1975]

hi, I went a little deeper on the working of the software wathdog of the ESP8266. Problem is the waiting on a response from a modbus slave (espacially during testing with no slave connected), during that time the software wathdog fires because it thinks the program hangs.

you can solve it elegantly by disabling the watchdog during modbus reads: ESP.wdtDisable(); result = node.readHoldingRegisters(15206,3); ESP.wdtEnable(1);

I have no more soft WDT resets anymore

Seems it works. Now it works more stable, haven't seen any WDT reset.