Siemens SIMATIC NET PROFIBUS manual Restrictions, Properties of the RS-485 Transmission Technique

PROFIBUS NETWORKS

Restrictions:

SDistance covered reduces as the transmission rate increases

SRequires 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:	1,000 m For transmission rates up to 187.5 Kbps
(depending on the cable	400 m For a transmission rate of 500 Kbps
type, see Table 3.1)	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-	Maximum 9
nected in series:
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”.

PROFIBUS Networks SIMATIC NET	1-11
6GK1970-5CA20-0AA1 Release 2 05/2000