Hi,

I have a Modbus connection established between Logo 8.3 (client) and S7-1200. My part is the Logo side. Data is storen in VM and I read it then using NAI and NI blocks. Almost everything works perfect except that approx. every 30 seconds all data goes zero. I see it in online test in Logo soft. Do you have any idea what could cause this behavior? Is it possible to see somehow incoming modbus datagrams in Logo soft to check the carried data? Thanks a lot!

Lukas

ixo65

Who pretends such nonsense?

For Modbus you can set data gathering interval, for S7 connection not. Imagine collecting data from remote location via NB-IOT or GPRS once per hour. Compared to Modbus, S7 protocol is "chatty" (3...30 kbit/sec, depending how much datapoints exchanged, this traffic goes constantly).

So please think twice before calling it an nonsense.

Depending on the application, it makes sense to prefer a ModeBus connection because of the "chattiness" of the S7 protocol.

lukas.v are you sure that the S7-1200 was configured as a ModBus server and is permanently providing data ?

lukas.v

 perfect except that approx. every 30 seconds all data goes zero. I see it in online test in Logo soft. 

 Try to set custom interval for modbus polling from Logo side. By default LOGO polls Modbus registers with 80 milliseconds interval, which is almost always unneccessary, 500msec (half second) or even more is enough for most applications. Hammering bus "as fast as i can" constantly may expose sometimes strange side effects.

ixo65

Not in the default settings, in default the intervall is not active (the time values are greyed out).

 

 Default polling rate is maximum, about 10-12 queries per second.