wrong data from serial instrument

[gerardoeeee]

I am using labview 5.1 to acquire data from a serial instrument(tachometer).The program is the one that is in the example of labview 5.1(LabVIEW<-> Serial)

the instrument has the following settings:
8 bits,no parity,1 stop bit,hardware control.
I am collecting some data from the tachometer,but the problem is that some data is incorrect.

USUALLY I OBTAINED THESE NUMBER IN THE COMPUTER:

6.94420
6.93955
6.94857
......
and suddenly the wrong data appear:
94
6.940(these two values in the box:read string)

(the value that is considered is 94 instead of the value i think is correct 6.94094).

Why does it happen that?
Is it a problem of data flow contol?
Is it relatad to the buffer size?

Thanks in advance for your ans
wer.

Gerhard Castro

[PdB]

Gerhard,

Most likely, your problem is that your application reads-out the serial port during a transfer of data.
So not all data from the tacho has reached the computer.
This is a common problem in serial com. and one of the reasons why certain protocols use a termination character to be sure that the string you print is in fact the entire string.

One simple solution is reading-out the number of bytes in the serial port. When this is a stable value, you can read serial port with the stable number of bytes.
How fast should you scan the number of bytes? Roughly 1/4 of the update rate of the tacho.

Another solution I use for more complex applications is an extra receive-buffer in LabVIEW to do string-scanning on. When I screw up my read on the
buffer, I always still have the original strings. Once you read-out your port and screw up, you've lost your data.

Hope this gets you going,

Patrick

[Ben]

Double check if the termination character is enabeld.

This could cause this problem.

Ben