Bench rig at school, TIA Portal V17, an S7-1200 CPU 1214C with a KTP700 Basic PN. It was all working last week, the panel showed the tank level and the pump state out of DB1.
Then I read a tutorial saying data blocks should be optimized, so I ticked Optimized block access on DB1, compiled and downloaded the PLC. Now every field on the panel shows ### instead of a number, though it still says connected and the icon's green.
I downloaded the HMI again and restarted the panel, no change there, and the connection in Devices and networks still points at the right CPU. Then I dragged the level out of DB1 into a brand new HMI tag and that one shows a value.
Screenshot of the tag table attached. Why would the old tags break and the new one work, am I missing something obvious?
V17 both sides, that's fine. Two things to rule out before the tags. Under Online and diagnostics on the panel, is the connection actually established or only configured? And what image is the panel on? If it's older than V17 you can get odd display faults after a download.
Connection's established, green in the diagnostics view. Panel image is V17, same as the project. Sorry if this is basic, two evenings on it now and no luck. The new tag works and the old ones don't, so I'm not sure it's the connection.
Are the old HMI tags addressed absolutely, like %DB1.DBW0?
Yes. The old ones say things like "%DB1.DBW0" and "%DB1.DBX2.0" in the PLC tag column. The new one I dragged in says "Tank".Level. Screenshot attached. Why does that matter?
Because an optimized DB has no absolute addresses at all. The CPU stores the variables where it likes and the panel can only reach them by symbol, so every HMI tag that says "%DB1.DBW0" has nothing to read and shows "###". Your dragged tag works because it's symbolic.
Two ways out. Quick one: DB1, Properties, Attributes, untick "Optimized block access", compile, download the PLC, and the old tags work again. Better one: keep optimized on and in the HMI tag table change each PLC tag from the absolute address to the symbol out of DB1, then download the panel. For a bench rig with a handful of tags, do the second.
I'd go with the second as well. The tutorial wasn't wrong for new projects, I reckon optimized is what you want on a 1200 anyway. I shipped machines for years with non-optimized DBs just so the panel tags kept their absolute addresses. My own default, and not a good one.
Fixed. First I unticked optimized to watch the values come back, and they did. Then I turned it back on and re-linked the eight HMI tags to the DB1 symbols, downloaded the panel, everything shows.
So it was the old HMI tags pointing at absolute addresses that an optimized DB doesn't have. Linking them symbolically sorted it.
One thing I still don't get: TIA compiled the HMI with no error at all even though those addresses were gone. Is that normal? Thanks kiran_s and tomhw.
Normal, sadly. The HMI compiler doesn't check PLC addresses.