mpi bus terminating

tny

Member
Join Date
Jun 2005
Location
usa
Posts
105
hi all,
i've been using simatic s7 200/300/400 series for nearly 4 years and i always connected my pg directly to the plc via siemens mpi cable as i learned from documents and i saw from others. today i had to connect to a s7 200 (i programmed it before) with my pg again but i couldn't connect. i changed the cable, (cable is siemens also), i changed the plc, i changed the pg! but i couldn't connect again.

finally 4 hours later, i tried to connect a pb connector to the plc side and pluged the mpi cable via it. (the pb connector with a db9 connector behind it) and turned on the terminating resistor.
it worked!
i still can not uınderstand how i could connect with only mpi cable before (with both of the siemens pgs)
does any one understand it?

thanks.
 
You have to turn on the terminating resistor only on both ends of the MPI-network. A network-connector can have an entry and an exit for the cable. Watch out for the 'arrow'. The last connector should have the cable comming into the 'entry'.
 
of course, but there is no such network. just a plc and a pg. i didn't need any other terminating device before till this problem. in all documents and courses, no one tells to use a terminator.
the siemens mpi cable has no terminating resistor also.
 

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