Correct Shared Variable behavior

I have a program, written in version 8.5, that has a shared variable used in an number of locations to shut down the program's major loops when the test system is being "shut down". I used a SV specifically to use its error in/out to force the execution order in these various loops. In 8.5 it has worked correctly, but yesterday I was helping my customer commision a new test system, using this program, and they only have 8.6, so we decided to migrate it all to this version. While still debugging the test system hardware we got an error which caused me to attempt to terminate the program. At this point I noticed that all but one loop had terminated correctly, and when I probbed the no terminating loop I discovered that it had had a hardware error, putting an error on the loop's error cluster. This caused the boolean Shared Variable to output a F rather than the T that had been written to it when I attempted the shutdown. This wasn't the behavior I remembered in my 8.5 version, so I created a quick little test, two parallel loops, one with the boolean SV in the write mode with a control to toggle it F/T the other loop having the SV in the read mode, with its output set to stop the loop if T. I had an error cluster shift register in the second loop, with the SV's error in/out connected to it that had a control to introduce an error in the error cluster. On the system running 8.5 writing a T to the SV stops the loop regardless of the error cluster state, but on 8.6 it does not, with the SV returning a F if there is an error present.
Has this been seen by others? Which is the correct behavior? I ended up doing a really quick change, making a "real global" and putting it into a case statement within a VI so that I could retain the ability to have the error in/out chain. I should have used a functional global, which is my normal mode rather than a "real global" but was tired and had just had an educational discussion with my customer about SV vs Globals and for the few minutes it took was in the "global mindset". I think it might be the first global I've used in a couple of years or more, I just was so flabbergasted about finding the apparent change in behavior.
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

IMHO if a function's behavior hasn't been specifically defined for 3 major release cycles, and it performs one way, it shouldn't be changed, regardless of some philosophical "standard". Pre-8.6 it behaved by passing the error through, but still performing its own task, output the value written to it elsewhere, so why would someone think that making this behavior change to "if an error is present output the default" would not have major implications? We don't all have the luxury of rewriting our projects from scratch. Worse yet, no where in the "release notes" , "known issues", "changes since 8.6", do I see this mentioned. I wouldn't have known about it, possibly for some time, if in debugging the test system hardware we hadn't had a hardware error (which hadn't occured in the prior three months of "ringing out" the hardware) that generated and error on the error cluster. The shared variable was in the various loops in my program to allow them to be stopped if an error was detected, or the operator was shutting down.
I would suggest that you use some type of "functional global" also called a LabVIEW 2 style global which uses a shift register on a while loop as the memory storage element in a while loop wired to execute only once (the stop node is wired "stop")rather than "real globals" unless you encapsulate the global in a sub-vi,. You can wire an error cluster straight through to allow the resulting vi to use the error chain for execution order control, as I had planned with the Shared Variable. You can also have a write case, read case, etc. inside the loop. Search on the this board for "functional global" or "LabVIEW 2 style" (there were no globals back then).
My fix at the moment is that I drove 250 miles (400 km) through a snow storm last night, am going in this morning and scrubbing the 8.6 based machine and installing 8.5.1 to make both machines identical. I would have done this originally (and not found out about this issue) but last week I forgot to pack my 8.5 DVD's and the customer only has the 8.6 ones at this time. They will be calling the NI office that handles them for their own, I suspect.
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Similar Messages

Shared & user-defined variable behavior when they are passed an error?

If a [TRUE] error condition is preset at its input terminal:
What is the expected behavior for a shared variable which is being read?             My guess: To return the default value for the datatype being read.
What is the expected behavior for a user-defined variable which is being read?     My guess: To return the default value for the datatype being read.
What is the expected behavior for a shared variable which is being written?         My guess: To not update the value of the variable.
What is the expected behavior for a user-defined variable which is being written? My guess: To not update the value of the variable.
Are my guesses at the behavior correct? If not, what is the real behavior? This is for LabVIEW version 11 and newer.
Thanks!
Solved!
Go to Solution.

Thank you Arham!   I'm sorry you had to go to the trouble of creating a test VI to get the answer. I thought that this might have been documented somewhere and I was just missing it. It still may be documented somewhere but sometimes creating a test VI is the quicker path to an answer than is a search for where the documentation is stored and the test VI is probably the more conclusive answer anyway.
In any case, thanks to your answer, it is now documented in a manner that should not be too hard for others to find, should they have the same question.
Thanks again.

Peculiar behavior of Shared Variable RT FIFO

I'm trying to "leverage" the enhanced TCP/IP and Shared Variable properties of LabView 8.5. My application involves (among other things) doing continuous sampling (16 channels, 1KHz/channel) using 6-year-old PXIs (Pentium III) and streaming data to the host. I developed a small test routine that was more than capable of handling this data rate, even when I had the host put a 20msec wait between attending to the PXI (to simulate other processing on the host). To do this, I enabled the "RT FIFO" property of the Shared Variable (which was an array of 16 I16 integers) and specified a buffer size of 50 (that's 50 arrays). Key to making this work was figuring out the "error codes" associated with the SV RT FIFO, particularly the one that says the FIFO is empty (so don't save the "non-data" that is present).
Flush with success, I started developing a more realistic routine that involves rather more traffic between Host and Remote, including the passing back and forth of "event" data. These include, among other things, "state variables" to enable both host and remote to run state machines that stay "in sync"; in addition, the PXI also acquires digital data (button pushes, etc.) which are other "events" to be sent to the Host and streamed to disk. I developed the dual state-machine model without including the "analog data" machine, just to get the design of the Host/Remote system down and deal with exchanging digital data through other Shared Variables. Along the way, I decided to make these also use an RT FIFO, as I didn't want to "miss" any data. One problem I had noticed when using Shared Variables is the difficulty of telling "is this new?", i.e. is the variable present one that has been already read (and processed) or something that needs processing. I ended up adopting something of a kludge for the events by including an incrementing "event ID" that could be tested to see if it was "new".
Today, I put the two routines together by adding the "generate 16-channels of integer data at 1 KHz and send it to the Host via the Shared Variable" code to my existing Host/Remote state machine. I used exactly the same logic I'd previously employed to monitor the RT FIFO associated with this Shared Variable (basically, the Host reads the SV, then looks at the error code -- a value of -2220 means "Shared Variable FIFO Read Buffer Empty", so the value you just read is an "old" value, so throw it away). Very sad -- my code threw EVERYTHING away! No matter how slowly the Host ran, the indicator always said that the Shared Variable FIFO Read Buffer was empty! This wasn't true -- if I ignored the flag, and saved anyway, I saw reasonable-looking data (I was generating a sinusoid, and I saw numbers going up and down). The trouble was that I read many more points than were actually generated, since I read the same values multiple times!
Looking at the code, the error line coming into the Shared Variable (before it was read) was -2220, and it remained so after it was read. How could this be? One possibility is that my other Shared Variables were mucking up the error line, but I would have thought that the SV Engine handling reading my "analog data" SV would have set the error line appropriately for my variable. On a hunch, I turned of the RT FIFO on the two Event shared variables, and wouldn't you know, this more-or-less fixed it!
But why? What is the point of having a shared variable "attached" to an error line and having it return "Shared Variable FIFO Read Buffer Empty" if it doesn't apply to its own Read Buffer? This seems to me to be a very serious bug that renders this extremely useful feature almost worthless (certainly mega-frustrating). The beauty of the new Shared Variable structure and the new code in Version 8.5 is that it does seem to allow better and faster communication in real-time using TCP/IP, so we can devote the PXI to "real-time" chores (data acquisition, perhaps stimulus generation) and let the PC handle data streaming, displays, controls, etc.
Has anyone been successful in developing a data-streaming application using shared variables between a PXI and and PC, particularly one with multiple real-time streams (such as mine, where I have an analog stream from the PXI at 16 * 1KHz, a digital stream from the PXI at irregular intervalus, but possibly up to 300 Hz, and "control" information going between PC and PXI to keep them in step)? Note that I'm attempting to "modernize" some Version 7 code that (in the absence of a good communication mechanism) is something of a nightmare, with data being kept in PXI memory, written on occasion to the PXI hard drive (!), and then eventually being written up to the PC; in addition, because the data "stayed" on the PXI, we split the signal and ran a second A/D board in the PC just so we could "see" the signal and create a display. How much better to get the PXI to send the data to the PC, which can sock it away and take samples from the data stream to display as they fly by on their way to the hard drive!
But I need to get Shared Variables (or something similar) working more "understandably" first ...
Bob Schor

Bob,
The error lines passed into and out of functions are just just clusters with a status boolean, an error code, and an error string, and are not "attached" to a particular function as you describe in your post. Most functions have an error in input and an error out output, and most functions will simply do nothing except pass through the error cluster if the error in status is True (to verify this for yourself, double click on a function such as a DAQmx Read or Write and look at the block diagram. If there is an error passed in, no read/write occurs). This helps prevent unwanted code from executing when an error does arise in your program. By wiring the error cluster from your other shared variables to your analog data variable, you're essentially telling LabVIEW that these functions are related and that your analog data variable depends requires that the other shared variables are functioning properly. The error wire is a great way to enforce the flow of your program, but you must always consider how it will affect other functions if an error does arise.
Anyways, it's great that you have things more or less working at the moment. Keep us all updated!

Shared Variable refuses to deploy correctly!

My problem seems like one that has been encountered before, but with no good answers on the NI documents or forums. When trying to run a VI that deploys shared variables, I keep getting an error that the shared variable engine cannot be found. This seems to be almost random, because I was able to deploy shared variables perfectly fine. It might have been when I restarted my computer that this problem started to occur.
I've tried disabling the firewall, that had no effect. LabVIEW 2009 reports the following when I try to run my VI:
"LabVIEW: (Hex 0x8BBB0005) Unable to locate variable in the Shared Variable Engine. Deployment of this variable may have failed.
This error or warning occurred while writing the following Shared Variable:
\\.\fake_data\flow_sh
\\.\fake_data\flow_sh"
I'll include all pertinent files so that you can see exactly what I'm doing. The purpose of the fake_data program is just to practice using shared variables, very simple. Thanks for any insight you can offer!
Solved!
Go to Solution.
Attachments:
fake_data.zip ‏145 KB

Is it possible you meant "net start ..." for the second command?
LabVIEW Champion . Do more with less code and in less time .

Polling variables using Modbus IP and labview 8.2.0 shared variables

I'm using shared variable in order to read/write register on a Watlow PM controller over Modbus IP standard. Once I make a change to FP control, the shared variable polling starts and I no longer get update of any controls or indicators on the FP.
Just wondering if this is an LV 8.2.0 issue and if any of this is addressed in LV 8.5?
Thx ahead of time
richjoh

Hi richjoh,
If I understand correctly, there are two issues to address: the status of the UpdateNow shared variable and the fact that your controls and indicators are not updating.
When you right-click on UpdateNow in your project and select Properties, what is the data type listed there? Is it bound to one of the other shared variables that has a value in Variable Manager?
After changing a control on the front panel, do you continue to see the values changing in Variable Manager even though the controls and indicators do not update on the front panel? Do you see the same behavior regardless of which control you change?
Thanks for the additional information.
Jennifer R.
National Instruments
Applications Engineer

Modbus ip shared variable network failure

I am using lab view 8.6 DSC module to communicate to a watlow system which contains five watlow 96 controllers and an EM gateway. I have created shared variables for the process temperatures and setpoints for each of the five controllers using watlow modbus register Numbers with a 400001 offset. I have also created shared variables for Updating,CommFail,UpdateNow,and UpdateRate which where predefined. I have error when starting the VI if the SV has been dragged and dropped into the block diagram. The message is Error -1967353902 (The Modbus I/O server failed to receive any response from the Modbus slave device.) occurred at SV in vi. If I bind a variable in the VI to this same SV the error does not occur but the variable cycles between Good, Network Failure, No known value, and device failure as stated in the variable manager watched variables. The Updating, CommFail and UpdateRate all have a consistent Good in the quality column of the variable manager. UpdateNow has X in value, type, timestamp, and quality columns. CommFail and Updating does cycle between true and false randomly. I have tried a third party software called SpecView 32 demo to see if the commincation with the modbus system is not working and I can create five watlow controlers on my screen and direct them to the ip address along with a unit address and the system works without faults. This leads me to believe the commincation bewteen the SV Engine and the IP address is not correct. HELP Please.
Robert Jensen
UND EERC

If your application can deal with it I would recommend staying clear of the 'Networked Published' option.
When I started my Modbus development on cRIO....I left it enabled, and with ~100 shared variables on a 9074, the CPU was railing, and I saw a buffering behavior on the shared variables (which was not desirable in my application).
In my application I am using the old modbus library (as apposed to the new API) for cRIO to slave comms, the cRIO being the master.
I am also using the IOserver making the cRIO a slave to an external SCADA - and it passes essentially the same data arrays as I use on the modbus library for my local HMI [Not an NI product].....Which is two full Modbus frame writes (@ 120 words each, and about 60 words more for ~300 words outbound from the cRIO).
The IOserver slave was a recent addition and did not add much to the CPU load - although only 16 bytes is high speed, the balance of the total word package is at either 1 second or 3 seconds.
So, in my experince, the 'Networked Published' option adds significant CPU loading (on entery level cRIOs) YMMV.
I am huge fan of the shared variable engine (some at NI were pusing the CVT, and TCE etc...). However most of my shared variables are not the Networked Published variety (excepting local module channels) those have remained networked published for DSM (Distributed System Manager) use.

Issue with use of shared variables in Crystal Reports 2008 Offline Viewer

Hi,
I have a report that contains a number of sub-reports which include drill-down functionality. The report returns data relating to an individual team with the user being able to view top level summary information in each area from the parent report and then drill into the sub-reports to view see more detail. The data returned by the sub-reports is filtered, using sub-report links, based on the team code parameter value given by the user. This parameter field resides in the main report.
One of the values returned by the main report is the team name. This is passed to each sub-report using a shared variable and each sub-report displays this team name as part of a heading.
This all works fine in Crystal Reports 2008, but when a report, containing data, is opened using Crystal 2008 Offline Viewer there is a problem with the shared variable. The value is displayed correctly when the user initially drills into the sub-report. However, when the user begins to drill into grouped data within the sub-report the value passed to the sub-report using the shared variable disappears.
How can I ensure that, when a report is viewed using Crystal Offline Viewer 2008, the value within the shared variable is not lost when users drill into grouped data within sub-reports
Thanks
Stuart

Please re-post if this is still an issue or purchase a case and have a dedicated support engineer work with you directly:
http://store.businessobjects.com/store/bobjamer/DisplayProductByTypePage&parentCategoryID=&categoryID=11522300?resid=-Z5tUwoHAiwAAA8@NLgAAAAS&rests=1254701640551

Print-time charting with shared variables on a report without groups...

hello all,
I have an interesting conundrum; I am working on a report (Crystal XI) with no groups to it, just several subreports. Presently the report is run weekly and sent to the manager of one of our departments.
The report itself showcases all areas of the department with total tasks, longest outstanding task, average days outstanding, MTD tasks completed, and YTD tasks completed. Due to the variety of tables the data pulls from, I have it set up as subreports that simply display the data.
All total, there are 20 different shared variables that have been obtained from 10 different subreports. I have the shared variables set as the running totals from the subreports (hence, all are print time). Since the running totals and all the subreports are time based and are not actually linked to ANYTHING on the main report, I am struggling with how to set up the formulas described in the white paper, "Charting on Print Time Formulas".
The setting up of the two formulas ({@onchngof} and {@showval}) will be different for my situation, as all of the subreports run off of date information relative to when the report is ran. I've got all of the subreports that the shared variables originate in early in the report; but where to from here?
Would I set up maybe a date grouping or some other non-essential consistent grouping to make it work? The way this report is, it really doesn't need grouping, because the main report is just a display agent for the subreports...
As always, any help is greatly appreciated!

Let me ask couple of questions before trying to resolve this.
1. The chart you are trying to built is placed in which section and is it on Main report or sub-report of its own. This is needed because if you are trying to access shared variables values in Main report, the section should be below the sub-report placed sections.
2. Try pacing few test formulas in Main report and make sure the correct values are being pulled in on Main report.
If you are successfully pulling the variable values on the report, try creating a simple chart in report footer with the values you have pulled and see if its taking you somewhere...
Would need more information on how those variables are being accessed form sub to main or sub to other sub for example are you making an array of those variables and splitting or bringing it in as separate...

How to use shared variables to address multiple Watlow controllers on the same COM port

Hello,
I am trying to use LabVIEW 2010 to control 4 Watlow temperature controllers on one COM port. 3 are Model 96 and 1 is an EZ zone controller. Each controller has a unique modbus address, and I am trying to read from and write to individual registers (such as closed loop setpoint) using shared variables. I am getting return data when reading (although the data appears to be invalid), but am unable to change the value in the register by writing. How can I be sure that the Modbus server is sending commands to the correct controller?
Chuck
Solved!
Go to Solution.

Peter,
Thanks for the reply. I have actually solved that problem. I realized that the Modbus server address has to be the same as the controller's Modbus address.
I have, however, run into another problem. Perhaps you could help me with that. I have a system with 4 Watlow controllers, 3 are series 96 controllers, one is PID only and 2 are ramping. The 4th controller is an EZ zone. I am using RS485 for communications and the controllers are all wired in parallel for communications and power.
I have set up 2 Modbus servers for 2 of the controllers.
This is the first I have ever worked with Modbus based communications. I have successfully programmed using the Modbus read/write VIs, and am wanting to move to shared variables. My questions right now revolve around addressing, Modbus I/O servers and COM ports. Specifically, at this point, I know the addresses need to match up between the server and the slave device (Watlow controller in my case), how many servers can I create and use on one COM port? If the number is limited, is there a way I can specify an address that I want the server to talk to? Will the broadcast mode work to request data values from the controllers?
I'd appreciate any information you can help me with, or if you could point me to some sort of concise 'How-To' for Modbus communication.
Thanks.
Chuck

Front Panel binding of shared variables very slow initialization / start

Hello @ all,
I am using a server running Windows2000 and LV 8 DSC RTS for datalogging. All shared variables are deployed on that server.
I am now facing the problem, that all front panels running on the clients using the network shared variables on the server take very long to sync on startup. First the flags on the controls bind to the shared variables turn red, after up to ten minutes they start to turn green. The panels use up to 40 controls bind to the shared variables.
All firewalls are turned off. I tried to connect the client to the same switch the server is connected to. Same problem. Does anybody have a clue?
Thx for your quick answers.
Carsten

While I can't offer any solution to your problem, I am having a similar issue running LV8.0 and shared variables on my block diagram (no DSC installed).
When using network published shared variables, it takes anywhere from 30 sec to 4 min from the vi start for any updates to be seen. Given enough time, they will all update normally, however this 4 minute time lag is somewhat troublesome.
I have confirmed the issue to be present when running the shared variable engine on windows and RT platforms, with exactly the same results.
In my case, the worst offenders are a couple of double precision arrays (4 elements each). They will normally exhibit similar "spurty" behavior on startup, and eventually work their way up to continuous and normal update rates. Interestingly enough there are no errors generated by the shared variables on the block diagram.

My project writes accelerometer data to usb drive but shared variables do not communicate with modbus

Hi there,
I have got a program that reads input from 3 off 9234 modules on a cRIO, the idea of the program is to read this data and save it in a bin file to a connected usb hard drive, the program also uses shared variables to connect the max signals from the 9234 then send thm to a modbus slave, my problem is that althought I am now getting the correct data on the usb drive I am not getting anything down the modbus link, I attach the program for you to see, all the shared variables are on the rt low speed loop, any help would be most grateful.
Many thanks
Jason
Solved!
Go to Solution.
Attachments:
logger 2plusmodbus2.zip ‏679 KB

Hi Jasonh,
Thanks for posting your code! Due to the lack of comments on the code, would it be possible to direct me to where it sends the code to the modbus slave please?
This tutorial on How to turn a RT Target into a Modbus Slave using IO Servers may also be of some help.
Kind regards,
Tori
Student

Dsc 8.2.1 cannot write to shared variables error 1950679035

I am getting error 1950679035 ni_tagger_write when I try to write to my shared variables. I recently upgraded from labview 8.2 to 8.2.1. I also upgraded to DSC 8.2.1. During the install, I had to upgrade my computer to SP2 (windows xp), which installed mdac 2.8 sp1 for use with dsc 8.2.1.
I have the windows firewall turned off, I checked with our IT dept and no upgrades were completed overnight (as the program worked yesterday using 8.2). I checked and MAX will get a connection with the fieldpoint unit. Everything is deployed from my machine, currently running under the dev environment.
I have looked at this thread, but I was not able to get anywhere, http://digital.ni.com/public.nsf/websearch/0D7B86F4B4D19A5E86256F9A006EECB1?OpenDocument and here.
Even though I have windows firewall turned off, I added all of the execptions to the windows firewall list.
It appears that the shared variable library is deploying correctly, as the the windows says that it has (when you run a vi). I am progmatically deploying the vi.
I looked at the variable manager and I attached a screenshot below. I am not sure if that means that it did not deploy correctly or not.?? (I was only watching a couple of the variables, I have about 20 total)
thanks
Kenny
Attachments:
variable manager.jpg ‏55 KB

It appears that my problem has been solved. Apparently our network had an internal error for a quick second and my nic did not like it. So after I restarted again (fourth of the morning) it started working now.
Kenny

Using a Meter control in LV Touch Panel, and using shared variables that are custom controls.

I Just started using LV touch Panel module with an NI TPC-2106.
I have two differenct problems:
1) I was planning on using the "Meter" control quite a bit. I can set up the meter exactly how I like on the host PC, but on the touch Panel computer it seems to ignore my adjustments, mainly the start and end of the scale - i.e. I would like control to run from 0 to 360 with 0 straight up, using the entire circle. However, on the Touch panel computer it always puts 0 at about 7 o'clock and 360 at about 5 o'clock. I have also tried adding markers to no avail.
2) I am communicating with a compact fieldpoint controller. I can creat a shared variable that is a simple double with no problems. However, I have some shared variables that use a custom control for the variable type - bascially a cluster with a couble doubles, a time stamp, and an enumeration. It lets me drag the shared variable into my diagram, but it seems to ignore it when I run it.

Ipshita_C,
- I am using LV 8.6.1f1and LV Touch Panel 8.6.1.
- I have attached a simplified VI that shows how I want to use the meter. Notice that the placement of the endpoitns does not work correctly on the touch panel, and that it ignores the arbitrary markers that I placed.
- I also have included an XY graph control that displays on the TPC with margins around the graph area that I removed from the graph control.
- For the shared variable, it appears to be an issue related to the touch panel, not fieldpoint. I found another thread in this forum that mentioned that clusters containing Enumerations do not work in shared variables on the touch panel. I changed the enumeration to an integer and it now works fine.
In general, there seem to be a disappointing number of limitations in the touch panel implementation. My biggest concern is that I have not found any documentation from NI that lists these limitations. I seem to have to try things out and see what works and what does not work. Can you point me to a comprehensive list of touch panel modules limitations?
Attachments:
test 2.vi ‏10 KB

Modbus Ethernet read and write to a Eurotherm 6180XIO Modbus server using LV8.2 shared variables

I am having EXTREME difficulty trying to establish communications with a Modbus device using LV8.2 shared variables. The device is a Eurotherm 6180XIO Datalogger configured as a Modbus master. The PC and a cFP-1804 are slaves. All IP addresses are set correctly. This approach using shared variables would seem simple, but I can't find any examples or proper guidance on how to get it working. I am trying to avoid having to mess around with TCP/IP, OPC, or any other old-fashioned method.
I have read many threads on related topics but none directly apply to this situation. I have created a library containing a Modbus I/O server and shared variables bound to read and write holding registers. I have followed all recommended tips for creating such variables but I can neither read or write data. All data types are U16 due to Modbus protocol limitations. I have also applied the LV x10 factor in the most significant digit in the register offset (6 digits instead of 5).
I have a cFP-1804 on the same network which reads into the datalogger OK. The registers I use are 31000 (for CH0 on module 0, 31002 for CH1, etc) and the data can be read as FLOAT32. I have updated the firmwate on the 1804 to the latest level. I cannot even get shared variables to read SGL values. Using registers 301001 for CH0 and 301002 for CH1 I can only read U16 values, and not a 2-word SGL.
Third party Modbus simulation software is able to write to and read from registers very easily, but not LabVIEW.
Some questions are:
- do I use a Modbus master or slave as an I/O server in the library as a target for binding the shared variables?
- is there some other wierd translation in register offsets between LabVIEW and traditional Modbus?
- is this actually possible using shared variables or am I wasting my time?

Sending the whole 60-character string using a string or array would be the most efficient. I have tried both methods, and these only cause the datalogger to flag a message log but no text is displayed.
For a string variable, I have used the following binding "My Computer\Modbus Test.lvlib\ModbusServer6180\442305", where ModbusServer6180 is a Modbus I/O server configured with the logger IP address, and 42304 is the register offset at the start of the text block in the logger. I need to write to 30 consecutive registers starting with this one. I am not using buffering and have not enabled single writer.
Can anyone confirm whether this method should work in 8.2?
Does the string need a special termination character?

Modbus and shared variable performance in large application

Hi all,
I am preparing to work on an application which is going to reading from up to 500 Modbus input registers on a CompactRIO over Modbus Ethernet using the LVRT Modbus IO Server implementation. I've put together some minor test VIs on the local network to test the Modbus connectivity and understand in the shared variable minding mechanism.
To save potential headaches in the future, do you all have any best programming/proejct management practices for using high channel count Modbus applications? Has anyone done high channel count testing (similar to the link below) but for shared variables bound to a Modbus I/O Server? Any caveats I should keep in mind?
Performance Benchmarks for Network Published Shared Variables
http://www.ni.com/tutorial/14675/en/
Thanks,
Chris
d2itechnologies.com

If your application can deal with it I would recommend staying clear of the 'Networked Published' option.
When I started my Modbus development on cRIO....I left it enabled, and with ~100 shared variables on a 9074, the CPU was railing, and I saw a buffering behavior on the shared variables (which was not desirable in my application).
In my application I am using the old modbus library (as apposed to the new API) for cRIO to slave comms, the cRIO being the master.
I am also using the IOserver making the cRIO a slave to an external SCADA - and it passes essentially the same data arrays as I use on the modbus library for my local HMI [Not an NI product].....Which is two full Modbus frame writes (@ 120 words each, and about 60 words more for ~300 words outbound from the cRIO).
The IOserver slave was a recent addition and did not add much to the CPU load - although only 16 bytes is high speed, the balance of the total word package is at either 1 second or 3 seconds.
So, in my experince, the 'Networked Published' option adds significant CPU loading (on entery level cRIOs) YMMV.
I am huge fan of the shared variable engine (some at NI were pusing the CVT, and TCE etc...). However most of my shared variables are not the Networked Published variety (excepting local module channels) those have remained networked published for DSM (Distributed System Manager) use.

Correct Shared Variable behavior

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