5.7.1 Addressing
Every device in the bus system is assigned a unique address. Valid addresses lie in the range 0...126, whereby 126 is the address of the delivery status. If the address is not set correctly, the device cannot communicate.
Networks with coupler or gateway
The PLC is able to assign up to 126 (0...125) addresses to individual participants at the bus. A device address may appear only once within a particular PROFIBUS DP system. If a segment coupler is used, then the addresses assigned to the PROFIBUS PA devices count as PROFIBUS DP addresses.
For a typical bus configuration with PLC and PC, the addresses are assigned as follows:
• the PLC is assigned an address (Class 1 master), typically address 1
• the PC or operating tool is assigned an address (Class 2 master), typically address 0 or 2
• the other addresses are assigned to the field devices.
Networks with links Links act as PROFIBUS DP slaves and receive their own address. The PROFIBUS PA field devices connected to link, however, form a separate PROFIBUS PA system. These are addressed separately.
The PROFIBUS DP addresses are assigned as follows:
• the PLC is assigned an address (Class 1 master), typically address 1
• the PC or operating tool is assigned an address (Class 2 master), typically address 0 or 2
• every link is assigned an address (e.g. addresses 3, 4, 5, 6, ...)
• the rest of the addresses are assigned to the other field devices that are connected to transporent segment couples or directly to the PROFIBUS DP system.
On the PROFIBUS PA side, the field devices connected to the link are assigned a unique address for the PROFIBUS PA segment of which they are part. They are not counted as part of the PROFIBUS-DP system
• every device is assigned an address between 3 and 125,
• the addresses 0, 1 and 2 cannot be assigned when the link is operating together with a standard master.
Examples for addressing are to be found in Sections 5.7.3 to 5.7.5
5.7.2 Cycle times
The cycle times must also be considered when the PROFIBUS PA segment is planned. Data exchange between a PLC (a Class 1 master) and the field devices occurs automatically in a fixed, repetitive order. The cycle times determine how much time is required until the data of all the devices in the network are updated.
The more complex a device, the greater the amount of data to be exchanged and the longer the response time for the exchange between PLC and device. Table 5-15 summarises the amount of data and the response times for Endress+Hauser devices. The total cycle time for the updating of network data is calculated as follows:
Total cycle time = Sum of the cycle times of the field devices + internal PLC cycle time
+ PROFIBUS-DP transmission time
When links or the transparent SK2 segment coupler are used, the total cycle time of a system can be reduced.
5.7.3 Example 1: Siemens segment coupler
Fig. 5-9: Network example for Siemens segment coupler
Siemens segment couplers 6ES7-157-0 AD81-0XA0 and 6ES7-157-0 AC80-0XA0, see Table 4-3, can be used by any PROFIBUS DP master (PLC or process control system) that supports a baudrate of 45.45 kbit/s. In the example, two couplers for hazardous areas and one for non-hazardous areas are used.
• A maximum of 126 (0 - 125) addresses can be given to the participants, since
• The segment coupler is transparent.
• 124 addresses are available for assignment to the field devices.
• The addresses 3 - 19 are used.
• The transmission rate is 45.45 kBit/s.
The cycle time for the following example is:
• Σ (cycle time of the devices) + PLC cycle time (ca. 100 ms)
= 17 x 10 ms + 100 ms
= 270 ms
!
Note!• For PROFIBUS DP alone, the DP transmission time must also be considered.
• The (bus) cycle time is the time period required under worse case conditions for the changes in input data to be transmitted to the master and the changes in output data to the slaves
Power supply CPU
100 ms
DP master
address A 1 Operating tool
e.g. FieldCare address A 2
PROFIBUS DP
PROFIBUS PA PROFIBUS PA PROFIBUS PA
Standard segment coupler Ex segment coupler Ex segemnt coupler
Explosion hazardous area
5.7.4 Example 2: Pepperl+Fuchs SK1 coupler
Fig. 5-10: Network example for Pepperl+Fuchs segment coupler SK1
The Peppert+Fuchs segment couplers KFD2-BR-EX1.PA and KFD2-BR-1PA.93, see table 4-3, can be used by any PROFIBUS DP master (PLC or process control system). The Segment coupler SK1 supports both cyclic and acyclic data exchange. It can thus be used in all common PLC or process control systems. In the example, two couplers for hazardous areas and one for non-hazardous areas are used.
• A maximum of 126 (0 - 125) addresses can be given to the participants, since the segment coupler is transparent.
• 124 addresses are available for assignment to the field devices.
• The addresses 3 - 19 are used.
• The transmission rate is 93.75 kbit/s.
The cycle time for the following example is:
• Σ (cycle time of the devices) + PLC cycle time (ca. 100 ms)
= 17 x 10 ms + 100 ms
= 270 ms
!
Note!• For PROFIBUS DP alone, the DP transmission time must also be considered.
• The (bus) cycle time is the time period required under worse case conditions for the changes in input data to be transmitted to the master and the changes in output data to the slaves
Power supply CPU
100 ms
DP master
address A 1 Operating tool
e.g. FieldCare address A 2
PROFIBUS DP
PROFIBUS PA PROFIBUS PA PROFIBUS PA
Standard segment coupler Ex segemnt coupler Ex segemnt coupler
Explosion hazardous area
5.7.5 Example 3: Pepperl+Fuchs SK2 coupler
Fig. 5-11: Network example for Pepperl+Fuchs segment coupler SK2
The segment coupler SK2 (1.PA with gateway KLD-GT-DP.1PA or KLD2-PL(2)-Ex1.PA with gateway KLD-GT-DP.1PA) supports both cyclic or and acyclic data exchange of the PROFIBUS DP V1 protocol. In the example, three segment couplers SK2 are used: two couplers for hazardous areas and one for non-hazardous areas.
• All data that is to be updated cyclically is automatically updated in the common data area by the PROFIBUS PA master.
• The update time depends on the data volume transferred via the PROFIBUS PA channel.
Cycle time From the point of view of PROFIBUS DP, the segment coupler represents a multi-slave device. If the PROFIBUS DP Master sends a request to a slave address existing at the segment coupler, the gateway answers directly on the request with the data, that are stored in the common data range.
Through this behavior, the PROFIBUS DP master does not need to wait for the PROFIBUS PA slave to respond. The result of this is that the cycle time of the entire system is calculated as follows:
tCycle = tCycle_PA-channel + tCycle_DP The time tCycle_PA-channel can be estimated as follows:
tCycle_PA-channel = 10 ms + n*10,5 ms + 0,256 ms*(LE + LA) where n = the number of PROFIBUS PA slaves
LE = total number of input bytes of all PROFIBUS PA slaves on the channel.
LA = total number of output bytes of all PROFIBUS PA slaves on the channel.
Power supply CPU
100 ms
DP master Operating tool
PROFIBUS DP
PROFIBUS PA PROFIBUS PA PROFIBUS PA
Standard power link Ex power link Ex power link
Explosion hazardous area
Segment 1 Segment 2 Segment 3
DP cycle time The time tCycle_DP can be estimated as follows:
tCycle_DP = TBit * n * 500 + 11*TBit*(LE +LA) where n = the number of PROFIBUS DP/PA slaves
LE = total number of input bytes of all PROFIBUS slaves LA = total number of output bytes of all PROFIBUS slaves TBit = bit time = 1/transfer rate
For the time tCycle_DP a safety add-on of 10% should be included in the calculation in accordance with the PROFIBUS User Organization.
The equation above applies given the following pre-conditions:
• The PROFIBUS DP network is operated as a monomaster system, i. e. there is only one master on the PROFIBUS DP. If you want to use a multimaster system, the token hold time and the corresponding pause times of the additional masters must be added to the total.
• Only acyclic data exchange takes place. If the master is also supposed to transfer acyclic telegrams, the time required for acyclic communication must be added in total.
Example The cycle time for the example in Fig. 5.11 is:
Σ1 (Cycle time of the PA network) = PA segment 1 + PA segment 2 + PA segment 3
where Σ1 = cycle PA segment 1 + cycle PA segment 2 + cycle PA segment 3
Σ1 = (10 ms + n*10.5 ms + 0.256 ms*(50)) + (10 ms + n*10.5 ms + 0.256 ms*(40)) + (10 ms + n*10.5 ms + 0.256 ms*(90))
Σ1 = 117.3 ms + 104.24 ms + 106.54 ms Σ1 = 328.08 ms
Σ2 (Cycle time of the DP PLC)
where
Σ2 = 1.165 ms + 100 ms Σ2 = 101.165 ms
tcycle = Σ1 + Σ2
= approx 430 ms 2
1
12---Mbit\s 24 500 11 1
12---Mbit\s×180
×
× +
×
+100m\s
∑
=5.7.6 Example 4: Siemens PA link
Fig. 5-12: Network example for Siemens DP/PA-link
The Siemens PA-link (6ES7-157-0 AD81-0XA0 with link 6ES7-157-0AA82-0XA0 or 6ES7-157-0 AC80-0XA0 with link 6ES7-157-0AA82-0XA0) can be used by any PROFIBUS DP master (PLC or process control system). Three links are used in the example, each with two segment couplers
• A maximum of 126 addresses can be assigned to the participants on the PROFIBUS DP system.
• A maximum of 122 PA addresses (address range 3 - 125) can be assigned in the PROFIBUS PA segments connected to each link.
• The PROFIBUS DP addresses 3 -5 are used to address the links.
• In the PROFIBUS PA segments, the addresses 3-11, 3-10 and 3-9 are used for the PA devices, whereby addresses 0 - 2 is reserved for the link in each case and not useable for PA devices.
• The transmission rate may be up to 12 Mbit/s.
The cycle time for the example is:
• Σ1 (Cycle time of the PA devices)
• For PROFIBUS DP alone, the DP transmission time must also be considered.
Power supply CPU
100 ms
DP master Operating tool
PROFIBUS DP
PROFIBUS PA PROFIBUS PA PROFIBUS PA
Standard segment coupler Ex segment coupler Ex segment coupler
Explosion hazardous area
Segment 1 Segment 2 Segment 3
6 Installation PROFIBUS PA
The chapter contains information on physical installation of the network. It contains the following sections:
• Cabling
• Grounding and shielding
• Termination
• Overvoltage protection
• Installation of the devices
• Setting the address