mpi/profibus operation on s7300

[yantrak]

hi all,

i would appreciate any help on the following.

1.how does the master check for(enumerates)the available devices on the bus.

2.how does the master interact with a device like pg/pc which is dynamic in it's presence.

3.in a token ring if a device disappears how is token passing assured.

thnx

 

[dchartier]

hi all,

i would appreciate any help on the following.

1.how does the master check for(enumerates)the available devices on the bus.

It doesn't; there is no lifelist.
The network configuration (for Profibus) or Available Nodes (for MPI)is created by the user (in the HWConfig and Netpro editors)and diagnostics are put in motion when they are not available for communication.

2.how does the master interact with a device like pg/pc which is dynamic in it's presence.

A PG/PC, an HMI station and a SCADA system are all considered masters class 2 (the DP master interfaces are Masters class 1) in Siemens' world. Masters class 2 do not hold a Profibus-DP configuration (like a PLCs' master class 1) but they can exchange and hold the token. When they recieve the token they can interrogate all masters class 1 on the bus (so they can program, download/upload, monitor or update tag values).

3.in a token ring if a device disappears how is token passing assured.

thnx

Token passing happens cyclically from Lowest station address to Highest station address, one address at a time. The next available master address answers when it is presented the token, and indicates it is being held. If a master disapears from the bus, it is bypassed because it dosen't answer. The token skips to the next responding master on the bus
If a slave disapears (or is unavailable) the master that holds it in configuration declares a BF and launches diagnostics. This does not affect the token passing.

For more information I suggest the Downloads section of Profibus.com.

Hope this helps,
Daniel Chartier

 

[yantrak]

thnx D.Ch.

but they can exchange and hold the token. When they recieve the token /QUOTE]

are all adresses passed the token irrespective of their presence?

if not then how will the current master know of the adress of the new entrant.

thnx agn

 

[dchartier]

Hello yantrak;
Look at my last paragraph, I believe I have already given you an answer on that.

Token passing happens cyclically from Lowest station address to Highest station address, one address at a time. The next available master address answers when it is presented the token, and indicates it is being held. If a master disapears from the bus, it is bypassed because it dosen't answer. The token skips to the next responding master on the bus.

Please come back if it is still not clear.

Hope this helps,
Daniel Chartier

 

[yantrak]

thnx D.Ch.

pardon me but what i get from you is the following.

1.token passing is only amongst masters.

2.each master holds the token as long as it wants.if there is a time limit then who arbitrates.i.e.who is overall master.

3.when a master is done with it's slaves it transfers the token to the next master adress.

4.this => that each master knows the next master.this info may not be available for masters like pg/pc to the configured masters.so either pg/pc brodcasts it's presence or there is some other mech. which will enable it's entry into the master circuit.

5.a master at adress 2 will pass token to 3,if there is no response then probably it tries for 4 ... in a sequence.is this the mech.

thnx for your patience.

 

[dchartier]

thnx D.Ch.

pardon me but what i get from you is the following.

1.token passing is only amongst masters.

Only masters will react to the token-passing telegram.

2.each master holds the token as long as it wants.if there is a time limit then who arbitrates.i.e.who is overall master.

The maximum access time for the token is calculated by the Profibus configurator. It needs to know lthe length of the bus (copper or fiber), the baudrate, the number of repeaters, and the number of masters (and what type)... This info is transfered to all slaves and masters as they come alive on the bus.

3.when a master is done with it's slaves it transfers the token to the next master adress.

A master class 1 will give up the token when its cyclic polls are done, and its acyclic data acquisition (diagnostics, record collection, profile telegrams sending)time is over.

4.this => that each master knows the next master.this info may not be available for masters like pg/pc to the configured masters.so either pg/pc brodcasts it's presence or there is some other mech. which will enable it's entry into the master circuit.

Your point 5 answers this very simply and accurately.

If a PG with address 0 comes on the bus, when token is passed to address 0 (as it will be upon reaching the HSA: highest station address on the bus) it simply picks it up... You can see that this will extend the bus time and slow down the bus. So the number of masters class 2 has a limit before disturbing Profibus-DP high-speed comms.

5.a master at adress 2 will pass token to 3,if there is no response then probably it tries for 4 ... in a sequence.is this the mech.

thnx for your patience.

 

[yantrak]

thnx D.Ch.

u were very hlpful and patient.
thnx agn