Hi All,
Good evening and I hope your well.
I am using LabVIEW 8.6 and VISA to write to a serial device. Baud rate is high (115.2k).
This device is generating an RF signal and is simply sending
messages to change the power of this signal. I am able to send one message to the
device successfully using LabVIEW and HyperTerminal. The problem comes when I wants to send multiple
messages. When I construct a string that contains 100 messages
separated by the EOL characters \r\n and does a single VISA write then
it takes about 2 minutes for the device to step through all of the
commands. When I write the same string to the device using another bit
of software eg. HyperTerminal it takes about 3 seconds.
The
serial device is connected to the LabVIEW computer via a serial
interface board and this has two LEDs on it (Tx and Rx). My monitoring
these LEDs I am able to get a bit more of an idea about what is going
on. When I send a string which only contains the termination
character \n both Tx and Rx the LEDs flashed instantaneously showing
the serial comms, this did not generate the required response though as
the device needs the termination \r\n. As soon as you use
the \r character, the Tx and Rx LEDs flash but then there is an
additional read that is done by the LabVIEW machine. This is what seems
to be slowing down the communications. This additional read is not
observed when using other software such as HyperTerminal.
I have the log files, but this is the summary:
Results:
0ms Delay Capture.spy
- 9:53:32.508 I start to send Labview info
- 9:53:37.789 Labview Closes the last VISA
HyperTerminal2.log
- 10:31:06 I start to send HyperTerminal Data
- 10:31:06 It finishes
I understand there are several differences between HyperTerminal and LabVIEW, namely speed and buffer size. But, I am not convinced this is causing this behavior on this one command which involves sending multiple messages. I have also seen the same issue with CVI - as LabVIEW. So this suggests to me its either the VISA layer handling the command differently to HyperTerminal, or LabVIEW requires the command to be altered firstly (which I guess could be speed..).
I am aware that Dennis in the past has recommended using HyperAccess but the cost is a factor at this point in time.
Another interesting piece of information, when HyperTerminal is set to emulation mode VT52 - the same results as produced with LabVIEW/CVI. The mode which works in HyperTerminal and is required is VT100. From what I have read, if it works in HyperTerminal then the battle is almost complete. But not in this case. Does anyone have any suggestions to find out what this extra read might be.. My knowledge of Terminal Emulation is amazing, but could escape characters be a factor?
Summary:
What is it about this mode that is being handled differently in LabVIEW (CVI) then in the Hyperterminal and is it related to this extra Rx?
Or, Is it more to do with the command I'm trying to send and the VISA layer?
Any thoughts or suggestions I'd be very grateful to here - I know a few of you out there have experienance (worked very closely) with VT100 emulation and with serial.
Kind Regards, and have a pleasant day.
J.
Message Edited by Gap.In.My.Knowledge on 01-15-2009 02:33 PM
