Siemens SIMATIC PCS 7 FOUNDATION Fieldbus Commissioning Manual page 45

Bus parameters Setting
range (de‐
fault)
Slot Time 1 - 512
(8)
Per DLPDU PhL Over‐ 2 - 63
head
(2)
Maximum Response
Delay
(10)
Minimum Inter DLPDU 0 - 120
Delay
(16)
Preamble Extension 0 - 7
(2)
Time Sync Class 0 - 7
(4)
FOUNDATION Fieldbus
Commissioning Manual, 02/2015, A5E32711026-AC
Meaning and limiting values
This parameter specifies how fast the FF device can reply upon receipt of a PDU.
The required setting can be derived from the EDD of the FF devices.
Assign parameters to this value in such a way that the minimum value is greater than
the maximum Slot Time of every FF device on the FF segment.
ST >= ST of each FF device of the segment.
The parameter defines the delay between the following data records of a connection
to the FF segment:
● End of the last octet
● Beginning of the first octet of other data records
1 - 11 This parameter specifies how fast the FF device can reply upon receipt of a PDU.
The required setting can be derived from the EDD of the FF devices.
● Determine requirement for each FF device:
MRD(FF device)=MRDST/ST
Assign parameters to this value in such a way that the minimum value is greater than
the ratio of Maximum Response Delay Slot Time and Slot Time of every FF device
on the FF segment.
● MRD(FF segment):
MRD >= MRD of each FF device of the segment
This parameter specifies the minimum interval between two frames on the FF seg‐
ment. Each FF device has a minimum value of MinInterPDUDelay. This value is
stored in the EDD.
Assign parameters to this value in such a way that it corresponds to at least the
maximum value of Minimum inter DLPDU Delay of all the FF devices on the FF
segment.
Minimum inter DLPDU Delay (segment) > max Minimum inter DLPDU Delay (FF
device)
The minimum value for this parameter is determined by the maximum value of all
the FF devices in the FF segment.
Each data record of an FF connection starts with a preamble octet which is used by
the FF devices (receiving nodes) for clock synchronization. The number of preambles
(s) can be extended when setting this parameter. The default value in PCS 7 is 2;
networks including digital repeaters may require larger values.
This parameter defines the quality of the clock accuracy of an FF device. Thus it also
defines the periods for time synchronization of an FF device.
The maximum value supported by an FF device is stored in the EDD.
Set this value to the lowest common class of all FF devices on the FF segment
(slowest time).
The value 4 corresponds to 1 ms.
Engineering
5.3 Parameter assignment
45