Back to basics: S7 TIA HMI to PLC comms

[DairyBoy]

Hello all. I have a numeric entry field on a KTP600 basic screen connected to a S71212 plc. When configured for input/output, it shows ### and when configured for input only, it will display the entered value on the screen but not in the plc.

First thing was to check for comms activity so I put a single "lamp" on the screen and allocated it to a cycling timer in the plc. That works.

Next try was a pair of buttons configured as "set bit" allocated to a self-holding rung's start/stop bits. Nothing doing.

So, two more indicators connected to M bits and toggle the bits: no change. But re-address one of them to the Q bit of a timer in the program and it works.

Only difference that I can see is that the first indicator that works is referenced to a physical output in the default tags table whereas all the others are in other tag tables that I have created (apart from the timer bit). I'm definitely picking them from the plc list in the popup and access & visibility in the hmi is checked.

What's going on here then?

Just added a numeric field to display a timer's ET. That works too.
But a M bit in the default tag table doesn't (set bit on press or invert bit).

 

[dcp325]

If you look at the tag table from the CPU, are "Visible in HMI" and "Accessible from HMI" checked? (Two colums just right from the address)

 

[DairyBoy]

dpc325, yes they are.

 

[dcp325]

Have you downloaded the program to the CPU since adding those tags?
I once had an issue after adding tags to the HMI the HMI would display ### instead of values, after recompiling and downloading the CPU the values appeared.

 

[DairyBoy]

Yes, I'm downloading every few minutes to both devices to try and resolve this.

Ha! now my indicator from Qo.o has stopped working and I haven't been near it...

so I added another lamp to the same plc address (Q0.0) and that doesn't work either.

 

[BryanG]

When I get weird stuff happening with things that should be simple, I tend to look outside what I am doing. Things like are the cables plugged in properly, have I got two things trying to use the same IP address, is a cable faulty.

 

[DairyBoy]

Yes, I know what you mean. New (screened) leads, new ethernet switch, 3 devices on the network: 192.168.0.1,2,10. It's totally bonkers, I just don't understand why it's only partial (well, most of it doesn't work).

 

[DairyBoy]

Bit the bullet and started over. I guess I was leaving a trail of confusion in the system as I was learning what not to do. Must have corrupted the hell out of it. One button, one bit: so far so good. Hope it continues that way...

 

[DairyBoy]

This is just nuts. Clean slate. New applications. 1 button on screen, no logic in plc. Monitor 1 bit from momentary pb on hmi. True/False as expected. Wrote 1 line of ladder (self-sealing coil with stop/start) and added the stop pb to the screen and a separate indicator to show the state of the coil. Downloaded both. Push the button. Nothing. Forced the start contact in the ladder and the coil latches on but no lamp on hmi. Very close to doing some real damage now.

3rd start over: 1 button on hmi. 1 tag in plc. Download. Press button. No response in data monitor.

 

[Jeff23spl]

have you tried to start from 0 with plc program also. it may be data overlap by having a word or double word overwriting the bit value you use etc...

make sure the data format is the same on both side and make sure you have just one connection called the same way on the HMI connection and hmi tag connection.

Usually when working both device in the same tia project, you will create the tag on the plc programming side and pick it up from there for the hmi project. This way, the tag keep it's same property.

 

[DairyBoy]

Thanks, Jeff23spl. I have started over several times now and always with a fresh project each time.

The latest version had one button: press to set M0.0 and release to reset M0.0. That worked (monitor only; no ladder). Then when I added tag M0.1 to the plc tag list only and downloaded that to the plc, the M0.0 bit stopped working! Subsequent deleting and reinstating doesn't fix it.

So, start again: new project. Declare 2 tags: M0.0 and M1.0. Test hmi pb with M0.0. OK in data monitor. Then add tag M1.1 and download s/w changes to plc. Now test hmi pb: M0.0 is stuck at 0.

 

[DairyBoy]

Update. Once the db is corrupted, even deletion of all tags in hmi & plc will not allow subsequent hmi pbs to work for any address, even direct to outputs (no ladder). But an hmi numeric read-only field monitoring a timer's ET register will display. So, maybe it's a plc-based read-but-not-write thing?

 

[DairyBoy]

All done

Well, thanks for the contributions. Turns out that it's a "known issue" with the comfort range of HMIs. And now it's a "known issue" with the basic range as well. The solution is to power cycle the plc and full comms is reinstated. I want my three days back!