Bus Parameters - Omron SYSMAC CS Series Operation Manual

A-1

Bus Parameters

The PROFIBUS Bus Parameters define both the baud rate and the bus timing settings, necessary to perform
the exchange of messages over PROFIBUS. The Bus Parameters settings must be determined for each and
every Master device on the bus, and usually depend on
• the number of I/O data bytes per slave device,
• the number of slave devices connected to the master,
• the number of other masters on the bus.
The Bus Parameter settings consist for one part of a number of settings, which are directly entered into the
PROFIBUS interface hardware registers. These settings implement the necessary timing to enable the transfer
of a single message between the PROFIBUS Master Unit and a slave device. The other part of the Bus Param-
eters must be calculated. These parameters implement the overall cyclic timing as well as the watchdog time to
monitor the communication.
The calculation is performed by the PROFIBUS Master Unit DTM. The software implements a formula to calcu-
late the settings which will be downloaded to the PROFIBUS Master Unit. Most of the parameters have baud
rate dependent default values. Some of the parameters can be tuned by the user. However, this is not recom-
mended, since the communication may not function correctly, due to incorrect settings or too small timing mar-
gins.
This appendix defines the parameters which are shown by the PROFIBUS Master Unit DTM, and provides the
formula used for the timing calculations.
A-2 Bus Parameter definitions
The figure below shows the PROFIBUS Master Unit DTM, Bus Parameter tab, in which the bus parameter set-
tings can be made.
Appendix A
Bus Parameters
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