Why does TP170 lose comms when I disconnect laptop from S7-224 ?

HEllo all !
I have got a TP170B (colour) connected to a S7-224 plc (only got 1 port) - so I am using a profibus cable (only 2 cores red & green) with "piggy back" connectors each end that have the terminating resistors in.

I have got comms on both the TP170 and the PLC set to PPI, 187.5kbps, highest station = 31,
PG/PC (Laptop) = node 0,
PLC = node 1
TP170 = node 2
I am using CP5511 pcmcia adaptor card in my laptop to connect to plc (PG/PC interface set to PPI comms as above)

I have the profibus/ mpi (its purple !) connected from TP170 to plc, and my laptop plugs into the top of the piggy back connector on plc.
Now whilst the laptop is plugged in and communicating with the plc, the TP170 screen is FINE ! But as soon as I power down Microwin or drop the connection to the PLC,or switch off laptop, the TP170 loses its connection and shows "no peer at address" !

Why is that !?

I have tried having the terminating resistors in various positions ON / OFF etc at either end of cable - but to no avail.

Also can someone please explain what the rule is exactly about when Terminating resistors should be on or off !? I find sometimes things work either way, and sometimes they DONT work in either position !
IF the terminating resistor is on the plug connected to the plc should it be ON or OFF ? SAme question applies to the HMI screen !?

Hope someone can shed some light on it for me,
Thanks,
STeve

STJ said:

Also can someone please explain what the rule is exactly about when Terminating resistors should be on or off !?

Click to expand...

Simple Rule--> If only one wire is going inside the connector then it (terminating resistor) should be ON, and if two wires are going inside the connector switch it OFF.


Your case HMI and PLC side should be ON (One wire both side). It should be communicating. Ok change your protocol to MPI and download and see.
Also when you goto Communication (In Microwin) and double click " Double click to refresh" then you should see both the address of your CPU as well as HMI. CPU address by default is 2, that of your laptop is 0 and for HMI it should be within 31.

Also there might be interference problem. Is HMI properly earthed? Your laptop when connected may be providing some sort of grounding hence HMI working, once you remove this indirect grounding communication goes with it.

Thats all I know
Manmeet

THanks for the reply !

You may be right about the earthing - the clamp is pretty rubbish in the connectors.. I will try that.

ANd I will try changing comms to MPI - someone told me to use PPI if I have a simple PLC to HMI link...

Regarding the terminating resistors :-

I understand that in a normal network the only terminating resistors that should be ON are of course those at the end of the network - hence only 1 cable going in.... does that apply also to the plc itself ?
Also what about those pass-through "piggy back" connectors :
I've got my purple profibus cable going into the plc connector and ALSO the cable from my PG/PC plugged onto the top of it - should that connector also have its resistor ON ? Am guessing YES as it is terminating the purple cable network whereas the PG/PC cable is "pass-through" into the PLC ??? IS that correct ?

Thanks again for the advice ! Much appreciated !

Steve

Hi there
Well Yes this applies to PLC also.
It shall be ON even if you have connected your laptop to Piggy back connector.

Good Day
Manmeet