Siemens SIMATIC NET PROFIBUS, Owner'S Manual, Page: 403 / 490

2.1 Non operating mode related functions
7
2 General Functions
Version 1.0 8/00
2 General Functions
Transmission rate
The PROFIBUS OLMs support all the transmission speeds (transmission rates) defined in the EN 50170 standard:
9.6 kBit/s, 19.2 kBit/s, 45.45 kBit/s, 93.75 kBit/s, 187.5 kBit/s and 500 kBit/s,
and additionally
1.5 MBit/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.
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 .
2.1 Non operating mode related functions
2.2 Operating mode related functions