Siemens SIMATIC NET PROFIBUS manual Topologies of RS-485 Networks, Transmission Rate, LAN Cable

Topologies of SIMATIC NET PROFIBUS Networks

2.1Topologies of RS-485 Networks

Transmission Rate

When operating SIMATIC NET PROFIBUS in the RS-485 transmission technique, the user can select one of the transmission rates below:

9.6Kbps, 19.2 Kbps, 45.45 Kbps, 93.75 Kbps, 187.5 Kbps, 500 Kbps,

1.5Mbps, 3 Mbps, 6 Mbps or 12 Mbps

Depending on the transmission rate, transmission medium, and network components different segment lengths and therefore different network spans can be implemented.

The bus attachment components can be divided into two groups:

SComponents for transmission rates from 9.6 Kbps to a maximum of 1.5 Mbps

SComponents for transmission rates from 9.6 Kbps to a maximum of 12 Mbps

LAN Cable

The transmission media used are the SIMATIC NET PROFIBUS cables described in Chapter 4. The technical information below applies only to networks implemented with these cables and SIMATIC NET PROFIBUS components.

Node Attachment

The nodes are attached to the LAN cables via bus connectors, bus terminals or RS-485 repeaters.

Cable Termination

Each bus segment must be terminated at both ends with its characteristic impedance. This cable terminator is integrated in the RS-485 repeaters, the bus terminals, the ILM and the bus connectors and can be activated if required.

Before the cable terminator can be activated, the component must be supplied with power. With the bus terminals and the bus connectors, this power is supplied by the connected DTE, whereas the RS-485 repeater, the ILM, and the terminator have their own power supply.

The RS-485 transmission technique allows the attachment of a maximum of 32 devices (DTEs and repeaters) per bus segment. The maximum permitted cable length of a segment depends on the transmission rate and the LAN cable used.

2-2	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000