Using USB to 8-port Serial : Looses Com session if attached equipment power cycled

[Scott.555]

I have a USB to 8-port serial converter to add additional comm ports to my PXI rack.

If I power the PXI rack and run Labview, then power the equipment attached to the USB Com port adaptor, I can get succesfull communication between PXI rack and attached equipment.

However if I re-power the attached equipment, the Com session appears to be lost and labview cannot communicate with it.

Shutting down labview the re-starting labview (just labview, not the PXI rack) and communication is re-established.

It has also been found that when communication is lost, that Hyperterminal also reports it cannot connect to this port when first run. Communication can be establishged once Hyperterminal is disconnect and reconnected.


Note : The RS232 link in question, only currently has Rx, Tx and Ground connected. Do I need DTR/DSR aswell ??

[Scott.555]

BTT

[Tristan_J]

Hi Scott,

Are you using a 2 of the NI USB-232/4 devices, or is the 8 port version from an alternative manufacturer? If you are using VISA to communicate with the ports it is possible that the resource has been locked. Try using the VISA close function on each of the COM ports in order to re-establish communication.

Let me know how you get on.

Kind Regards

Tristan
Applications Engineer
National Instruments UK & Ireland

[Scott.T]

I have solved this by using VISA commands Open/Close/Read/Write to control/read RS232 traffic, rather then using the Serial Drivers supplied with Labview.

Thanks anyway...

P.S It is not a NI USB - RS232 converter.

[webster]

Hello,

I have two questions to NI USB-232/4.

[1] Question 1:

I have 8 sensors whose interface is RS-232.
Thus it seems to me that I need two NI USB-232/4 to connect them to my PC (transmit/receive data between PC and the eight sensors). 

Or NI can provide a 8-port RS232 to USB?

[2] Question 2:
I am a user of LABVIEW 8.0.  Does NI provide LABVIEW library (code) to
write to (read from) 8 sensors through the 2 sets of USB-232/4?

Anybody doesn't have any problem the NI USB-232/4 and its library?

Thanks.

[Dennis_Knutson]

1. NI doesn't have an 8-port USB-RS232 though other vendors do. I use an 8 port from Vscom and though it's not as nice as the NI product, it only cost about $100 if my memory is right.

2. All the drivers that NI has can be found at http://www.ni.com/devzone/idnet/default.htm. You can do a search but the majority of drivers are for instruments and not sensors.