Siemens SIMATIC NET PROFIBUS manual Non operating mode related functions

2 General Functions 2.1 Non operating mode related functions

2General Functions

2.1Non operating mode related functions

Transmission rate

The PROFIBUS OLMs support all the transmission speeds (transmission rates) defined in the EN 50170 standard:

9.6kBit/s, 19.2 kBit/s, 45.45 kBit/s, 93.75 kBit/s, 187.5 kBit/s and 500 kBit/s, and additionally

1.5MBit/s, 3 MBit/s, 6 MBit/s and 12 MBit/s.

The transmission rate is set automatically as soon as the PROFIBUS OLM receives a frame. The setting or adjust- ment is dependent on the transmission rate and the set operating mode. Depending on the OLM, this can last a maximum of between 0.5 s (at 12 MBit/s) and 5 s (at 9.6 KBit/s).

If the transmission speed has not been recognized, the outputs of all ports are blocked. If the transmission rate changes during operation, this is detected by the modules, which then automatically adjust their settings accordingly. Transfer malfunctions may temporarily occur while the rate is being altered.

Signal regeneration

The modules regenerate the signal form and amplitude of the data received. This allows up to 122 PROFIBUS OLMs to be cascaded (limited by the address space in PROFIBUS networks).

Help when setting up

At least one bus subscriber must be switched on and active in order to check the optical fiber connections during the installation. This bus subscriber serves as the frame source. The PROFIBUS OLMs act passively when it is switched on. They recognize the transfer speed from the frames sent by the bus subscriber. An optical help when putting the device into operation is provided by the port LED which then lights up.

2.2 Operating mode related functions

The operating mode is set using switches located on the top of the module. A sticker attached to the side of the module provides assistance with the settings.

Segment monitoring at the RS 485 port

If the operating mode ”Electric port with segment monitoring“ is set, each receiver monitors the RS 485 bus segment connected to it for faulty frames or continuously busy networks. If faulty frames are received by the receiver, or if the network is busy for longer than the maximum permitted send time, forwarding of the received signals is blocked until frames can be received again correctly, or if no signal is received for one second.

The RS 485 bus segment is not monitored in the operating mode ”Electric port without segment monitoring“. Interference from the electrical segment affects the entire network.

Please observe the installation notes in 4.4.3. ”Connecting the electrical RS 485 bus lines“, p. 22 .

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