Reading reply from serial port returns empty when read/write commands run separately

I have a serial port that is configured as such: Serial Port Object : Serial-COM3

   Communication Settings 
      Port:               COM3
      BaudRate:           9600
      Terminator:         'CR'

   Communication State 
      Status:             open
      RecordStatus:       off

   Read/Write State  
      TransferStatus:     idle
      BytesAvailable:     4
      ValuesReceived:     306
      ValuesSent:         200

(BytesAvailable shows 4 because the snapshot is right after I had written to the port).

If I run the following commands in a function without entering debugger or if I simply enter them simultaneously in the matlab console, the read function returns an expected result, almost instantly

fprintf(this.serial_, '%s', command); fread(this.serial_, nBytes);

IF, however, I print the command, and then afterwards try to read it, the read results in the following:

Warning: Unsuccessful read: The specified amount of data was not returned within the Timeout period.

ans =

   Empty string: 0-by-1

Any thoughts on why the serial reply is different?

Thanks!

[Austin Adam]

Hey did you ever figure this out? I'm having the same issue where I send a command just as you did, and upon reading the response, I get an emtpy 0x1 matrix.

I have used this exact method before to communicate and it worked every time, but now for some reason I am having issues... is there something you did that made it start working again?

[Walter Roberson]

It is not clear to me that a terminator is being sent?

Answer 1

[riverCN]

I got the same problem. Just add a pause between writing and reading. This is called the port latency. A pause(0.05) should do the trick.