Questions about BRX?

[Mike Nash]

Oh wait! You mean MyMadeUpMemBlk123 will be accessible from Cmore? Sometimes, even if slower that could be huge.

Will it be slower only if the Cmore is on a screen that needs it (or it is in a graph or "script")?

[BobO]

Sooo, I could stick with the old driver and avoid the hit on the scan time? Or am I being overly cautious?

Probably being overly cautious. Depending on how much work is being done there may not be a noticeable difference...but...worst case I'm sure you can see it.

I get lots of ribbing from ADC techs about my paranoid attitudes regarding design choices and performance. What can I say, I'm an engineer. I worry so you don't have to.

[BobO]

Oh wait! You mean MyMadeUpMemBlk123 will be accessible from Cmore? Sometimes, even if slower that could be huge.

That is precisely what I mean.

Will it be slower only if the Cmore is on a screen that needs it (or it is in a graph or "script")?

No. Just a comm function; only processed when requested.

The pain is simply that you have to parse the element string and search the memory configuration to determine where in memory it is. It's all binary searches and as fast as it can be. In practical terms, it's probably not an issue 90% of the time...but...doing the same painful work over and over every comm offends my engineering sensibilities. I tried to get them to go the route of "send me the textual request (once) and I'll translate to the high performance request", but that apparently wasn't going to drop into their design very well. When goaded with the "well, other more respectable PLCs do it that way", I gave in.

[BobO]

I probably should also mention that the size of the memory configuration greatly affects the performance of the symbolic driver. I tested with 230+ blocks and 1000+ heap items. I don't remember the actual numbers, but just imagine the worst case of searching for a single field in a program block structure (~150 fields) located in the heap (~1000 items). And then filling the entire C-more screen with the maximum number of items, and each item is that worst case lookup. A full request of dozens of those worst case searches can mount up.

In practice, you're probably searching through a tiny fraction of that, and your C-more screens are not worst case. But again, I worry so you don't have to. This kind of engineering decision is precisely the kind of thing that my forum tag line is referring to, and is a fundamental part of Host's design culture. We try real hard to avoid things that we know have the potential to be less than optimal.

In this case, there are no surprises. Use the full featured and more flexible driver. If you encounter issues, fall back to the higher performance answer. Options are good.

[franji1]

Oh wait! You mean MyMadeUpMemBlk123 will be accessible from Cmore?

The C-more export facility in Designer (File->Export->Element Documentation...) was enhanced so that you could export structure field names (e.g. MyPID.PV) for taking advantage of this new/better C-more driver, along with user blocks like MyMadeUpMemBlk.

See the attached screen shot from Designer 2.0, specifically the new radio button C-more... WITH Struct Fields Content Format option.  The other C-more radio button is for the "old" driver.

[Controls Guy]

Can you store a program on an SD card and load it into a BRX without a PC?

I don't think I saw anything about that in the Updates file.

[BobO]

Can you store a program on an SD card and load it into a BRX without a PC?

Not yet, but a definite consideration. I would probably use some variation of a DMLoader image. Biggest question is how to trigger it. DIP switch? Magic handshake? Other?

[Controls Guy]

You could.  I think most brands, if there's an image on the backup/loading media, just load it.  That's what Siemens does, although in their case you have to dedicate a given SD card for transferring program, additional memory, etc., whatever it's going to be used for, so on power up the PLC already knows the SD card is transfer type and just loads the project.

If you did that, it would be like PLCs equipped with program backup EEPROMs that if one is present on power up, automatically load the program, sometimes depending on the settings in the PLC.  A SLC, for example, has several levels of eagerness to load from the PROM, Always Load, Load If There's No Program in RAM, and so on.

If you do implement that (fully automatic mode), there should be some kind of option for not loading data along with code, in case it's a normal power cycle with an already running PLC, and the SD card is just there for emergency program backup.

[BobO]

I thought about that approach too, but felt it was kinda heavy handed. If others have done it, it's certainly an easy approach.

The DMLoader utility lets you define exactly what's in the image.

[Controls Guy]

Sounds like the best way to get there.  Thanks!

[Dean]

Question about the file system instructions. Say you wanted to do a running average like the simple example I attached. Rather than counting and moving data, would it be possible to just pull a chunk of data points out of a log file, do the math, step forward one row, pull another chunk, do the math, lather, rinse, repeat?

[BobO]

Question about the file system instructions. Say you wanted to do a running average like the simple example I attached. Rather than counting and moving data, would it be possible to just pull a chunk of data points out of a log file, do the math, step forward one row, pull another chunk, do the math, lather, rinse, repeat?

Certainly.

[mhw]

Most of y'all aren't shy, but if anyone has any questions about BRX they are afraid to ask, don't be! We'd love to hear from you!

In previous versions of DMD you could change an element's address to a different address in the same memory type by only entering the number. For example to change C1 to C2 you could type 2. This doesn't work anymore. Was that by design? It's not a big deal, I will eventually get my brain trained.
I am unable to add a POM to the offline dashboard configuration. Am I missing something?
I need a feature chart with BRX models and prices down the left and features across the top. It took longer than I wanted to wade through the extensive product selection to find what I wanted.
The ability to have two Ethernet or two serial ports is great.
I love the way you allow the analog to be scaled in the dashboard. Its great to have the raw and the scaled values available.

[BobO]

In previous versions of DMD you could change an element's address to a different address in the same memory type by only entering the number. For example to change C1 to C2 you could type 2. This doesn't work anymore. Was that by design? It's not a big deal, I will eventually get my brain trained.

It's working for me. Not every field supports that ability, due to the need to support constants. If there is a specific field where that has changed, please let us know. It might be a bug, or it might be due to some other change.

I am unable to add a POM to the offline dashboard configuration. Am I missing something?

The POM is just shown online for status purposes. All of the required configuration is always there regardless of whether there is one installed or not. Is there something you are trying to do that you are unable to?

I need a feature chart with BRX models and prices down the left and features across the top. It took longer than I wanted to wade through the extensive product selection to find what I wanted.

That's a great idea. I've never bought one through the website, but I felt it needed some kind of overview matrix.

The ability to have two Ethernet or two serial ports is great.
I love the way you allow the analog to be scaled in the dashboard. Its great to have the raw and the scaled values available.

Glad you like it!

[Mike Nash]

In previous versions of DMD you could change an element's address to a different address in the same memory type by only entering the number. For example to change C1 to C2 you could type 2.

I wondered what that was!