Siemens SIMATIC NET PROFIBUS User Manual

Page 21

PROFIBUS NETWORKS

1-11

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

Restrictions:

Distance covered reduces as the transmission rate increases

Requires additional lightning protection measures when installed outdoors

Properties of the RS-485 Transmission Technique

The RS-485 transmission technique in PROFIBUS has the following physical
characteristics:

Table 1-1

Physical Characteristics of the RS-485 Transmission Technique

Network topology:

Bus, tree structure with the use of repeaters

Medium:

Shielded, twisted pair cable

Possible segment lengths:
(depending on the cable
type, see Table 3.1)

1,000 m For transmission rates up to 187.5 Kbps

400 m For a transmission rate of 500 Kbps
200 m For a transmission rate of 1.5 Mbps Mbps
100 m For transmission rates of 3.6 and 12 Mbps

Number of repeaters con-
nected in series:

Maximum 9

Number of nodes:

Maximum 32 on one bus segment
Maximum 127 per network when using repeaters

Transmission rates:

9.6 Kbps, 19.2 Kbps, 45.45 Kbps, 93.75 Kbps, 187.5 Kbps, 500 Kbps, 1.5
Mbps, 3 Mbps, 6 Mbps, 12 Mbps

Note

The properties listed in 1-1 assume a bus cable of type A and a bus terminator
according to the PROFIBUS standard EN 50170–1–2. The SIMATIC NET
PROFIBUS cables and bus connectors meet this specification. If reductions in the
segment length are necessary when using special versions of the bus cable with
increased d.c. loop resistance, this is pointed out in the sections on
“Configuration” and “SIMATIC NET PROFIBUS Cables”.