Data Transmission Times Between Mdt And Controller; Transmission Times With Profibus - Bosch Rexroth ID 40 Manual

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Bosch Rexroth AG, MIT: ID 40, 3 842 530 344/2014-05
PROOF COPy 1 | 20.05.2014 | FOR INTERNAL USE ONLy

13.3 Data transmission times between MDT and controller

The application program reads data from the MDT via the SLK and writes data via the
SLK to the MDT. Aside from the amount of data, the times required for transmitting
data from the controller via the read/write head to the mobile data tag depend on
the following, fieldbus-specific factors:
• SLK function used. If data is read using event-oriented data exchange, the
controller does not need to send a read command via command-oriented data
exchange
• PLC cycle time, which executes the read and write commands and transfers the
MDT data from the fieldbus master to the application
• Fieldbus system bitrate.
• If the positioning of the MDT and SLK fall within the tolerance limits, the
effective data rate between SLK and MDT can drop due to frequent repetitions
• If the system is used in extremely low EMC environments, the data rate between
SLK and MDT can drop. Additional shielding steps may have to be taken for the
SLK in such applications (e.g., functional grounding as described in the assembly
instructions).
13.3.1

Transmission times with Profibus

Additional factors affecting the data transmission time with Profibus:
• I/O module configuration from the GSD file. A 128-byte I/O module for command-
oriented data exchange has a higher data rate than, e.g., a 16-byte module for large
amounts of data. In the latter case, significantly more bus cycles are required
• Number of users on the bus. The lower the number, the higher the data
throughput of each.
• Type of additional users on the bus. Users with greater latency time also delay data
access to the SLK
The measured values in the following table were obtained by a Bosch PCL
controller with a PLC cycle of 10 ms, a 128-byte I/O module for command-oriented
transmission and a 12 Mbps PDP transfer rate.
SLK and MDT communicated under standard conditions:
Frontal position, 6 mm gap, no sources of interference.
Table 51: PDP data transfer times, 10 ms PLC cycle
Byte count 8
Read [ms] 16
Write [ms] 17
The measured values in the following table were obtained by a Bosch PCL controller
with a PLC cycle of 2 ms. The other test parameters are the same as above.
Table 52: PDP data transfer times, 2 ms PLC cycle
Byte count 8
Read [ms] 14
Write [ms] 16
16 32 64
19 40 78
20 45 86
16 32 64
16 24 36
20 28 44
256 1024 7664
160 640 4740
220 860 6280
256 1024 7664
145 546 3800
176 690 5006