Siemens Welding System ST PCS 7 User Manual

PROFIBUS PA

Siemens ST PCS 7 · November 2007

9

■

To create a smooth network transition between PROFIBUS DP 

and PROFIBUS PA, the SIMATIC product range offers two ver-

sions: the DP/PA coupler and the DP/PA link. 
The following criteria can be applied when choosing the network 

transition:
• DP/PA coupler: 

For small quantity frameworks (volumes of data) and low tim-

ing requirements; limiting of data transfer rate on the 

PROFIBUS DP to 45.45 kbit/s

• DP/PA link: 

For large number of stations and high cycle time require-

ments; data transfer rate on the PROFIBUS DP up to 12 Mbit/s

■

The two DP/PA routers are based on two versions of the 

DP/PA coupler: 
• Ex [i] DP/PA coupler (max. output current 110 mA)

for implementation of PROFIBUS PA networks with a line or 

tree topology in environments up to Ex zone 1, not for redun-

dant architectures (coupler redundancy, ring) 

• FDC 157-0 DP/PA coupler (max. output current 1000 mA)

for implementation of PROFIBUS PA networks with a line, tree 

or ring topology in environments up to Ex zone 2; can be used 

for the redundant architectures "Ring" and "Coupler redun-

dancy"

DP/PA couplers are also integral components of the DP/PA link 

(see design). The DP/PA link connects PROFIBUS DP and 

PROFIBUS PA together, and decouples the transmission rates. 

In contrast to the DP/PA coupler which limits the data transmis-

sion rate on the PROFIBUS DP to 45.45 kbit/s, the DP/PA link 

does not influence the performance of the PROFIBUS DP. 
The DP/PA link functions as a slave on the PROFIBUS DP and as 

a master on the PROFIBUS PA. From the viewpoint of the host 

PROFIBUS DP master, the DP/PA link is a modular slave whose 

modules are the devices connected on the PROFIBUS PA. Ad-

dressing of these devices is carried out indirectly via the DP/PA 

link which itself only requires one node address. The host 

PROFIBUS master can scan devices connected to the 

DP/PA link all at once.
If the router is a DP/PA coupler, the nodes on the PROFIBUS PA 

are directly addressed by the PROFIBUS DP master (controller). 

The DP/PA coupler is an electrical node, but is transparent for 

communication between the master and PA field devices; it 

therefore does not require setting of parameters or addresses 

(exception: FDC 157-0 DP/PA coupler used as PROFIBUS diag-

nostics slave).

FDC 157-0 DP/PA couplers configured as PROFIBUS diagnos-

tics slaves supply extensive diagnostic and status information 

via PROFIBUS for swift location and clearance of faults:
• I&M data (Identification & Maintenance) 
• Current and voltage values on the main cable
• Redundancy status
• Wire breakage
• Short-circuit
• Signal level
For this purpose, each FDC 157-0 DP/PA coupler requires its 

own PROFIBUS address. This applies independent of use in a 

DP/PA link or as a DP/PA router.
The DP/PA link and DP/PA couplers as DP/PA routers can be 

mounted on an S7-300 profile rail. They are operated with 24 V 

DC, and can be installed in environments up to Ex zone 2 with 

extended temperature range.

© Siemens AG 2007