PROFIBUS Manual

An RS 485 repeater amplifies the electrical signal on a bus line and supplies electrical isolation between individual bus segments.

 

A repeater must be used if:

 

a)more than 32 stations must be connected on one bus

b)individual segments on the bus must be isolated

c)or a relatively long distance must be connected.

 

A repeater must know the bit rate used by the bus in order to change over the direction of amplification at the right time. It can do this by adjusting the bit rate until it can recognize correct signs. In this way it is possible for the repeater to identify the bit rate independently.

 

This adjustment process last a certain time, during which the repeater function is not guaranteed. For this reason, depending on the product, it is also possible to adjust the bit rate on repeaters manually with a switch.

 

A repeater does not have a station address, unless it has the capacity to transmit diagnostic information. A diagnostic repeater of this type will be assigned a station address.

 

Depending on the product used, only a limited number of repeaters may be switched between two stations. This means that a maximum of n+1 segments can be switched consecutively. This product-dependent limit is n = 3, 4 or 9. For repeaters with the necessary signal regeneration, this limit can be disregarded.