ProSoft Technology PTQ-PDPMV1 - Manual (Page 217)

PTQ-PDPMV1 ♦ Quantum Platform Hot Standby Support
PROFIBUS DP Master Network Interface Module for Quantum User Manual
ProSoft Technology, Inc. Page 217 of 306
August 12, 2014
7.4 PTQ-PDPMV1 Master Bus Properties for Use of a P&F DP/PA
Segment Coupler
7.4.1 PROFIBUS DP Time Behavior
The segment coupler supports both cyclic and acyclic data exchange of the
PROFIBUS DPV1. Cyclic communication services are performed based on a
specific time grid, which is referred to as the bus cycle time.
A bus cycle time (or cycle time for short) is the worst-case-scenario time required
to transfer input data from a PROFIBUS slave to the PROFIBUS Master, or
output data from the PROFIBUS Master to the slave. All data that is to be
updated cyclically is automatically updated in the common data area by the
PROFIBUS PA Master.
The cycle time required depends on the volume of data that is transferred via the
PROFIBUS PA channel. From the point of view of the PROFIBUS DP, the
segment coupler represents a multi-slave. If the PROFIBUS DP Master sends a
request to a slave address existing at the segment coupler, the gateway answers
the request directly with the data that is stored in the common data range.
Consequently, the PROFIBUS DP Master does not need to wait for the
PROFIBUS PA slave to respond. Therefore, the cycle time of the entire system
is:
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 all output bytes of all PROFIBUS PA slaves on the channel
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 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 conditions:
 The PROFIBUS DP is operated as a mono-Master system, i. e. there is only
one Master on the PROFIBUS DP. If you want to use a multi-Master 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 into the total.