DS1487 Datasheet, PDF (6/8 Pages) National Semiconductor (TI) – Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver

Applications Information (Continued)
Due to the multipoint nature of the bus, contention between
drivers may occur. This will not cause damage to the drivers
since they feature short-circuit protection and also thermal
shutdown protection. Thermal shutdown senses die tem-
perature and puts the driver outputs into TRI-STATE if a fault
condition occurs that causes excessive power dissipation
which can elevate the junction temperature to +150˚C.
A typical multipoint application is shown in the following fig-
ure. Note that termination is typically required but is only lo-
cated at the two ends of the cable (not on every node). Com-
monly pull up and pull down resistors may be required at one
end of the bus to provide a failsafe bias. These resistors pro-
vide a bias to the line when all drivers are in TRI-STATE. See
National Application Note 847 for a complete discussion of
failsafe biasing of differention buses.
DS012920-16
www.national.com
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