modbus-webserial / Smoke test (64 words / 64 bits)

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- Connect opens a WebSerial Modbus RTU client.
- Apply (in settings) re-opens the client using the current settings, reusing the same port.
- Start runs a full "runOnce()" test cycle repeatedly.
- Delay below is applied only between cycles.
- If repeated errors: apply interRequestDelay of a few ms

Loop interval: 1.0 s
WebSerialConfig
Port: none

Preview below is the exact object passed to ModbusRTU.openWebSerial(opts).
CRC policy only chooses strict vs resync; maxResyncDrops is always set to the default. 


      

    


    

      
    
        
  1. 
          Holding registers (0 ā€“ 63)   0
        
    2. 
          ā€¢
        FC 16
        bulk-write
        64 words
        0ā€¦63
    
          ā€¢
        FC 03
        bulk-read verify
    
          ā€¢
        FC 06
        single-write each word (reverse order)
    
          ā€¢
        FC 03
        read back in 8-word chunks verify

        
  2. 
          Input registers (0 ā€“ 63)   0
        
    3. 
          ā€¢
        FC 04
        one-shot read all 64
    
          ā€¢
        FC 04
        8-word chunk reads (8Ɨ8)
    
          ā€¢
        FC 04
        64 single-word reads ā€” compare all three results

        
  3. 
          Coils (0 ā€“ 63)   0
        
    4. 
          ā€¢
        FC 0F
        write-multiple T F T F ā€¦ pattern
    
          ā€¢
        FC 01
        bulk-read verify pattern
    
          ā€¢
        FC 05
        toggle each coil individually
    
          ā€¢
        FC 01
        8-byte chunk reads verify new pattern

        
  4. 
          Discrete inputs (0 ā€“ 63)   0
        
    5. 
          ā€¢
        FC 02
        one-shot read all 64
    
          ā€¢
        FC 02
        8-byte chunk reads (8Ɨ8)
    
          ā€¢
        FC 02
        64 single-bit reads ā€” compare all three results
      


      Errors appear with their sub-step tag (e.g. ā€œ3-cā€), counters tick
      after each major step completes without error.
    


    

    

    

      
        Example Arduino sketch (ATmega32u4 over USB CDC, 64 regs/64 bits)
      
      
#include <Arduino.h>

// Some AVR cores don't define HAVE_CDCSERIAL even though USBCON exists.
// This makes ModbusRTUSlave(Serial_&) available on ATmega32u4 (Leonardo/Micro/Pro Micro).
#if defined(USBCON) && !defined(HAVE_CDCSERIAL)
  #define HAVE_CDCSERIAL
#endif

#include 

constexpr uint8_t  SLAVE_ID = 1;
constexpr uint32_t BAUD     = 9600;

/* 64-word / 64-bit data areas */
uint16_t holdingRegs[64];
uint16_t inputRegs  [64];
bool     coils      [64];
bool     discretes  [64];

// Force USB-CDC serial (Serial_) on 32u4
ModbusRTUSlave mb(Serial);

void setup() {
  Serial.begin(BAUD);

  // Don't block forever; browser opens the port when ready
  unsigned long t0 = millis();
  while (!Serial && (millis() - t0) < 2000) {}

  mb.configureHoldingRegisters(holdingRegs,  64);
  mb.configureInputRegisters  (inputRegs,    64);
  mb.configureCoils           (coils,        64);
  mb.configureDiscreteInputs  (discretes,    64);

  mb.begin(SLAVE_ID, BAUD, SERIAL_8N1);
}

void loop() {
  mb.poll();
}
  

    

        

      
        Example Arduino sketch (SAMD21 over USB CDC, 64 regs/64 bits)
      
      
#include 
#include 

constexpr uint8_t  SLAVE_ID = 1;
constexpr uint32_t BAUD     = 9600;

uint16_t holdingRegs[64];
uint16_t inputRegs[64];
bool coils[64];
bool discretes[64];

ModbusRTUSlave mb(Serial);

void setup() {
  Serial.begin(BAUD);

  unsigned long t0 = millis();
  while (!Serial && millis() - t0 < 2000) {}

  delay(100);   // helps USB CDC settle

  mb.begin(SLAVE_ID, BAUD);

  mb.configureHoldingRegisters(holdingRegs, 64);
  mb.configureInputRegisters(inputRegs, 64);
  mb.configureCoils(coils, 64);
  mb.configureDiscreteInputs(discretes, 64);
}

void loop() {
  mb.poll();
}