Uploading comments in ladder?
- Thread starter EVriderDK
- Start date
Steve Bailey
Lifetime Supporting Member + Moderator
Many of the current models of PLC store the comments. There is still a large installed base of older PLC models where that is not the case.
Because they take up gobs of memory, which has been a limited resource until recently.
By retaining the source file.
This comment confirms you know next to nothing.
Please enlighten me
Trust that there are reasons for everything, and ignore what your brain thinks.
Manglemender
Member
I'm sure that by now the OP is probably regretting how he/she phrased his/her question.
People growing up with the modern convenience of smart phones and the internet have no concept of what went before or what really goes on inside a computer.
Another common confusion is "why did you write all that using integers rather than reals?" This fails to appreciate that some older PLCs were not able to do floating point arithmetic and even if they did, it takes 4 times longer and has less precision than a double integer.
A typical line of code make use up 10-20 bytes of memory. The associated comments might occupy 100 - 200 bytes. Memory is (was) expensive and the comments are of no use to the PLC.
Nick
People growing up with the modern convenience of smart phones and the internet have no concept of what went before or what really goes on inside a computer.
Another common confusion is "why did you write all that using integers rather than reals?" This fails to appreciate that some older PLCs were not able to do floating point arithmetic and even if they did, it takes 4 times longer and has less precision than a double integer.
A typical line of code make use up 10-20 bytes of memory. The associated comments might occupy 100 - 200 bytes. Memory is (was) expensive and the comments are of no use to the PLC.
Nick
Ronnie Sullivan
Member
But - Mitsubishi have allowed comments to be downloaded with the program for 20 years.
It's a real boon to come across an old Mitsi plc and when uploaded see that comments are in there.
You can share memory between the program size and comments.
It's a real boon to come across an old Mitsi plc and when uploaded see that comments are in there.
You can share memory between the program size and comments.
rdrast
Lifetime Supporting Member
/shrug. Comments aren't "All That" any way. Code gets modified, usually the comments are not updated.
A Design Document though, is useful, as it gives the goals of a system without delving into the bit by bit details.
And, if you can't follow the code, you shouldn't be monkeying with it.
A Design Document though, is useful, as it gives the goals of a system without delving into the bit by bit details.
And, if you can't follow the code, you shouldn't be monkeying with it.
Manglemender
Member
The term "old" is relative. What may seem old to you may still be considered modern to some of us!
Please don't misunderstand me. Having comments and symbols downloaded with the code is a good thing for sure; I was trying to explain why they weren't in the past.
Mitsubishi have always been innovative with their PLCs. My first PLC experiences were with Mitsubishi kit back in the mid 1980s and the handheld programming terminal was in statement list and displayed one instruction at a time: no ladder and certainly no comments! We would draw the ladder we wanted on a piece of paper and then write the matching STL underneath before entering it one instruction at a time.
Nick
Thank you for the answers everyone.
Paulus. Ok, if they were 15 years old I could understand, but PLC's like brand new Siemens s7 300/400 also ? Couldn't these comments be loaded into a separate flash memory or something like that. It should be very inexpensive. We don't have time to distribute source files etc all the time. Step7 PLCs are used, so who has thr most recent source file ? It is a mess.
Why would I be talking about old PLCs ?
No, there is definately not always a reason for why things are as they are. - Can you go to the supermarket and buy an old nintendo? No, it is outdated.
- People who are new in some area usually knows next to nothing, so ? Without new people I guess there would not be as much of a use for a forum like this.
The only reason for why I am asking is simply that my fellow automation engineer colleagues and Google could not answer my question.
rdrast, surely, the engineering team will be instructed to use comments. Everything else would be a loss of money to the company.
This is why I don't understand why the PLC manufactureres just keeps producing the old stuff and not making important upgrades like including a small flash, or making the PLCs smaller in size etc.
But well, people are buying it, so why change
Paulus. Ok, if they were 15 years old I could understand, but PLC's like brand new Siemens s7 300/400 also ? Couldn't these comments be loaded into a separate flash memory or something like that. It should be very inexpensive. We don't have time to distribute source files etc all the time. Step7 PLCs are used, so who has thr most recent source file ? It is a mess.
Why would I be talking about old PLCs ?
No, there is definately not always a reason for why things are as they are. - Can you go to the supermarket and buy an old nintendo? No, it is outdated.
- People who are new in some area usually knows next to nothing, so ? Without new people I guess there would not be as much of a use for a forum like this.
The only reason for why I am asking is simply that my fellow automation engineer colleagues and Google could not answer my question.
rdrast, surely, the engineering team will be instructed to use comments. Everything else would be a loss of money to the company.
This is why I don't understand why the PLC manufactureres just keeps producing the old stuff and not making important upgrades like including a small flash, or making the PLCs smaller in size etc.
But well, people are buying it, so why change
just the cowboy
Member
This is why I don't understand why the PLC manufactureres just keeps producing the old stuff and not making important upgrades like including a small flash, or making the PLCs smaller in size etc.
But well, people are buying it, so why change
After working with PLC's for 35 years they did come down in size big time. But they have started to get so small they are fragile and don't hold up, so smaller is not always better. When PLC's started using programming devices they were high tech at 6MHz processors and 6 meg hard drives, gives you and idea of how hard it was to program, every thing had to be streamline so it would fit.
Programming has come full circle also, I started with BASIC for HMI programming then went to object based, now with CODesys things are going back to programming language again.
Too fragile is of course also not good.
Maybe they should try making the design in a whole new way. They can take up a lot of space in a cabinet those things
Of course, many years back, memory would be costly. Everything was costly 20 years ago.
You ARE talking about old PLCs. The I'm not sure on the exact timeline, but I'd bet they were launched 20+ years ago.
PLC manufacturers keep producing the old stuff, because they have promised their customers to continue to support existing installations for 10+ years. Backwards compatibility and legacy support are a huge drag on progress in every industry, but it is especially true in our industry. Rockwell is in the process of discontinuing a PLC line they introduced in the 80's, and their loyal customers are in an uproar.
In the cell phone market, change happens very fast. My wife's phone is 3 years old, and her fav apps keep breaking. V2.0 worked ok, but when the app updated to V3, it requires a newer phone, so she can't update. However, the servers require the app to be updated, so the old version doesn't actually do anything any more. In the consumer space, no one really cares. If this happens in the industrial space, plants go down, at the cost of a million dollars a minute.
But well, people are buying it, so why change
Siemens did change. They launched the S7-1200/1500, which has exactly the feature you request.
Oh, that is good knowledge. So they are at least working towards it
So I'm not totally off when saying that it would be a good feature with some more memory.jgreenewv
Lifetime Supporting Member
To mk42's comment, the S7-300 was new around 2000, so the platform is at least 16 years old at this point. It's generally not considered cost effective for the manufacturers to design upgraded processors for their older platforms to give the kinds of features you're asking about. They've dumped their R&D money into the next big thing (in this case the 1200/1500.)
In a situation like this, they really can't win. Rockwell can't continue to support the older SLC processors, they discontinue them, people complain. They don't update the SLC to be able to store comments, people complain. They release a new platform with all of the nifty new features everyone wants, at an increased price to cover development of those features, people complain. As much as I like to bag on them for some of their business and design decisions, they're in a bit of a no-win situation in a lot of areas.
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