Siemens 420 manual USS bus configuration via COM link RS485, 30 RS485 Terminator

3 Functions Issue 07/04

3.7.1USS bus configuration via COM link (RS485)

Using MICROMASTER with RS485 communication requires a proper termination at both ends of the bus (between P+ and N-), and correct pull up/ pull down resistors at least one end of the bus (e.g. from P+ to P10, and N- to 0 V). (refer to Fig. 3-30)

Fig. 3-30 RS485 Terminator

When the MICROMASTER drive inverter is the last slave on the bus (refer to Fig. 3-31), and there are no other pull up/pull down resistors on the bus, the supplied terminator must be connected shown in Fig. 3-30).

Last Slave

Master

e.g. PLCRS485 Terminator

First Slave

RS485 Bus

RS485 Terminator

Fig. 3-31 USS bus configuration

When the MICROMASTER is the first slave on the bus (refer to Fig. 3-31) the RS485 Terminator may be used to terminate the bus by using P+ and N- only, for the bus is powered by the last drive as explained.

NOTE

The supply for the pull up/ pull down resistors must be available whenever RS485 communication is in progress!

MICROMASTER 420	Operating Instructions
98	6SE6400-5AA00-0BP0