Application Notes - Omron SYSMAC CS Series Operation Manual

F-1 Introduction
This appendix contains an application note regarding the use of a special ladder program to detect any CS1/
CJ1W-PRM21 PROFIBUS Master Unit failures. This programs specifically covers failures due to faulty bus
parameters, set by the user.
F-2 Application Note Background
The CS1/CJ1W-PRM21 Master DTM allows the user to change certain bus parameter, in order to further opti-
mize the PROFIBUS network performance. The risk however in doing this is that certain combinations may
lead to failures in the communication, either direct, or at a later point in time. The direct result of this failure is
that communication between the Master Unit and the PLC CPU - the PLC I/O refresh cycle - will take longer
than anticipated.
A ladder program can now be used to detect this, if the application warrants this safety measure. It relies on
the fact that non-used software switches (see section 4-2-1 Software Switches 1 (Word n)) when set by the
user program, are always reset by the Master Unit.
F-3 Application Program
The ladder program, as shown in the figure below, will regularly set switch number 15 in the Software Switches
1 word (CIO Word n, where n in the example is 1500), and start a counter. The counter will count the amount
of PLC I/O refresh cycles, before the Master Unit resets the switch. If the counter reaches the maximum value
(e.g. 40 as in the example ladder program), without the switch being reset, a PLC error will be generated.
The counter must be configured by the user, and depends on the PROFIBUS cycle. The longer that cycle is,
the longer the counter has to count up. It is recommended to include a safety margin to avoid the PLC error
being generated too soon. An estimate for the value can be made using the formula below.
Timer value = Max ( 40, ----------------------- )
In the ladder program shown as example below, the minimum value of 40 has been used. The unit number for
the example Unit is 0.
Appendix F

Application Notes

2*
T
TR
min. PLC Cycle
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