master slave advantages?

hey guys! i was wondering why did profibus adopted the master-slave exchange of data? it is the most efficient way?

For example if i had a profibus-dp network with 5 stations (pc + 2 master + 2 slaves) all connected and with the termination resistors on at the end of the segment:

What happens if some of the slaves devices turns off (say plc s7-200 shutdown)? this will interrupt the bus? I have read the profibus profiles and understand that is always a linear bus topology with token ring media access control, so if some trouble appears in any station obviously(because of linear bus) the bus will fail!......am i correct?

How can i solve that? Did the master-slave method ensures some kind of safety data?

Cheers to all!

No, the bus does not fail, and yes there is safety built in.
This is 20 years proven technology.
The 'linearity' does not mean that the telegrams are passed between each node. The master yells and all the slaves listen. The adressed slave responds if it exists.

If you are really interested in profibus, you will find lots of info here: http://www.profibus.com/📚

Kalle

thanks KalleOlsen for the answer, but i just found the method of access (token ring, polling) depending on the profibus dp class. I couldn´t find info about advantages, or why they adopt master-slave and not server-client or other ones?
Can you specify where are those manuals or books?
Thanks a lot for your help!

Aha, archeology?

As I can recall there were (are) 4 different Profibus protocols, FMS, FDL, PA, DP. All exept PA running on RS485. Profibus DP was mainly based on Sinec L2 from Siemens. There was a rat-race between Fieldbus Foundation and Profibus to win the market, so it was maybe more important to get something that already worked out, than to spill time and make more sophisticated specs. I cannot tell you why this and not that solution was chosen, but I guess it was market share and big money.

http://en.wikipedia.org/wiki/Profibus

Kalle

If you want to have a look at a really impressing io-data transmission tech., you should check out Ethercat.
http://www.ethercat.org/
Kalle