Troubleshooting PROFIBUS

The RMC and RMCTools provide several tools for troubleshooting the PROFIBUS communications.

LED

An LED on the RMC indicates that a PROFIBUS connection has been made and the RMC is exchanging data with the PROFIBUS master. On the RMC75P, this LED is labeled Net. On the RMC150 PROFIBUS module, this LED is labeled Comm Status.

This LED should be solid green. If it is flashing or flickering green, it indicates an intermittent connection, generally caused by a parameterization or configuration error.

This LED may be off for any of the following reasons:

Wrong slave address set in the RMC
Wrong slave address set in the PROFIBUS master
Incorrect GSD selected in the PROFIBUS master
PROFIBUS master has not been configured to include this slave
Incorrect parameterization sent by the PROFIBUS master
Incorrect configuration sent by the PROFIBUS master
PROFIBUS master not active
Improper PROFIBUS cable or connector
Incorrect PROFIBUS cable termination
RMC is powered off
PROFIBUS master is off

PROFIBUS Connection Status Register

The PROFIBUS Connection Status register provides PROFIBUS connection information to user programs. This register is located at:

RMC75P: F21:6

RMC150: F45:6

This register has one bit defined, which can be used within the RMC user programs as part of handling broken connections:

Bit	Description
0	Connection Established. This bit will be set when the PROFIBUS interface is in the Data Exchange mode.

Event Log

The Event Log Monitor can be used to view the PROFIBUS data. By default, the Event Log only records the changes in the PROFIBUS connection state or address. However, the Event Log Filter can be configured to make a log each time there is a change in the data sent from the PLC to the RMC.

Using the Event Log for the I/O Modes

To log the incoming PROFIBUS data, set the Event Log Filter as follows:

In the Project pane, right-click Event Log and choose Properties.
Click the Communications folder and click PROFIBUS.
Check the I/O Mode Data Logging and click OK. The Event Log will now log an entry each time the PROFIBUS data changes and will display the data.

Using the Event Log for the Basic/Enhanced Modes

See the topic for the respective Basic/Enhanced mode for details.

Communication Statistics

The Communication Statistics Window provides information on the PROFIBUS settings and connection, including which parameterization and configuration data was last sent to the RMC.

PROFIBUS Timeouts

How long will it take for the RMC to detect that the PROFIBUS connection is broken?

This is controlled by the PROFIBUS master.

Specifically, when the master sends the Set_Parameters message as one of the required steps to enter DATA-EXCHANGE mode with the slave device, the second and third bytes in that parameterization are called WD_Fact_1 and WD_Fact_2. These two 8-bit values are multiplied together and then by 10ms to give a timeout value. Therefore, the master can make this value as short as 10ms and as long as 650 seconds (>10 minutes!).

The user must determine how to set this value for their particular PROFIBUS master.