AN1348 - APPLICATION NOTE

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5. APPLICATIONS

A typical ST485 application is the network allowing the connection of up to 32 devices; termination

resistances are tied only on the first and last unit and the value depend on the line impedance (54Ohm or

120Ohm), see figure 5. By connecting a node to the line, a stub is created and its length should be lower

than 15cm (6inches) to avoid transmission problems.

Figure 5: Typical RS-485 Line

In order to avoid wrong data transmission and signal reflections all the transceiver should be connected

sequentially among them, like figures 6b and 6d (6a and 6c are bad configurations).

Figure 6: Typical Network Connections

D

R

D

R

Stub length

Stub length

D

R

D

R

6a.

6b.

6c.

6d.