A problem about reading from serial port

Question

Hi,
   I just sent '0x03' from MCU to PC continuously, and then sent  '/n' as a stop character after every '0x03'. I use labview to read the data. The problem is when it get two '03' it get a '0', another two '03' and another a '0'. I don't know where is the '0' from?
  PS: Hyper terminal can display natrually.
   Thank you! 
帖子被hengfo在08-08-2007 10:14 PM时编辑过了
Attachments:
serial read.vi ‏36 KB

Answer 1

I think the problem may be the loop reading the serial port is running too fast.  There is no timing delay in the loop, so you are reading it as fast as you can, and probably faster than the device is sending data.  So sometimes the buffer is empty, and then the empty string gets converted to a numeric zero.  The way to know for sure is to put an indicator on the error wire coming out of the serial port read.  I bet you will see errors about the read buffer being empty.
Put a wait timer in the loop to slow down the execution just slightly.  This is a good idea so that LV doesn't eat up all the CPU resources.  Look at the example for Basic Serial Write and Read.  You may want to have a loop ahead of the read that waits until there are a certain number of bytes at the port before it reads the serial port.  You may want to put a loop around the serial port that waits until a valid number is read in before it exits the loop and goes to the numeric conversion.
Message Edited by Ravens Fan on 08-09-2007 08:50 AM