Feature request: VISA serial locking 
Author Message
 Feature request: VISA serial locking

Hi folks,

My application uses a hand full of devices, which are mainly controlled
by serial interfaces. Some of them share a RS485 bus. I use VISA to
prevent the black magic needed with the serial vis.

A good style of programming is to have all communication in parallel
wires and separate vis for each device (See the error cluster
thread). I have to ensure that only one vi talks to its device at one
time. Other vis and devices on the same bus have to wait until the
first vi has completed communication or all data becomes garbled. VISA
GPIB does this with lock/unlock. I tried the lock/unlock vis with
serial VISA. It did not work. After digging deep into the VISA
programmer manual for several hours I found that it is not
implemented. Why?

Putting all vis into a big sequence is not the labview way to do it.

I dont need shared locking with 'passwords', only plain, unshared
locking. I have to implement this via semaphores myself. Why hasnt NI
done that?

A good device example is a HP power supply with a GPIB and serial
interface. It has commands to read and both voltages and
currents. Good programming practice dictates using different vis for
voltages and currents. On the GPIB interface (pseudo) parallel
execution of both vis is possible by using locking. But it is not
possible to use the same vis with serial VISA. VISA portability
between interfaces doesnt work here. Thats a major drawback not
stated anywhere.

IMHO this by itself is worth a fix for LV 5.1. It is not a feature. It
is a bug.

How do you think?

Johannes Niess



Sun, 13 Jan 2002 03:00:00 GMT  
 
 [ 1 post ] 

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