c# Serial port losing trailing character -

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i have modbus interface in project. have 2 serial ports on pc, 1 on board , 1 usb serial. if use on board serial port miss last character of return string, if use usb serial port whole return string.

//onboard--------

tx: 01 03 02 00 00 12 c4 7f
rx: 01 03 24 00 00 00 64 00 00 00 0c 00 00 00 00 06 fa 02 d0 d9 54 00 00 00 00 00 04 00 0c 00 00 00 0c 00 00 00 00 00 00 c6

//usb serial--------------

tx: 01 03 02 00 00 12 c4 7f
rx: 01 03 24 00 00 00 64 00 00 00 0c 00 00 00 00 06 fa 02 d0 d9 54 00 00 00 00 00 04 00 0c 00 00 00 0c 00 00 00 00 00 00 c6 e9

if using datareceivedhandler event:

private void datareceivedhandler(object sender, serialdatareceivedeventargs e) {     int rxcnt = 0;     serialport sp = (serialport)sender;      (rxcnt = 0; rxcnt < _serialport.bytestoread; rxcnt++)     {         rx_buffer[rx_buffer_len++] = (byte)_serialport.readbyte();     } }

same code running on 2 different ports different results, ideas? regards richard

something found... flush in & out buffers before transmit modbus message. if don't flush rx_buffer see missing character @ start of next received packet: tx: 01 03 02 00 00 12 c4 7f rx: 01 03 24 00 00 00 64 00 00 00 0c 00 00 00 00 06 fa 02 d0 d9 54 00 00 00 00 00 04 00 0c 00 00 00 0c 00 00 00 00 00 00 c6

tx: 01 03 02 00 00 12 c4 7f rx: e9 01 03 24 00 00 00 64 00 00 00 0c 00 00 00 00 06 fa 02 d0 d9 54 00 00 00 00 00 04 00 0c 00 00 00 0c 00 00 00 00 00 00 c6

i don't understand why character comes through next message because there 1000ms delay between 2 messages

_serialport = new serialport();

        _serialport.portname = ports.elementat(0);         _serialport.baudrate = 9600;         _serialport.parity = parity.none;         _serialport.databits = 8;         _serialport.stopbits = stopbits.one;         _serialport.handshake = handshake.none;         _serialport.readbuffersize = 250;         _serialport.receivedbytesthreshold = 1;           _serialport.datareceived += new serialdatareceivedeventhandler(datareceivedhandler);         try         {             _serialport.open();         }         catch         {             this.close();         }

device manager port setup}


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