DS1487N NSC [National Semiconductor], DS1487N Datasheet - Page 6

• Manufacturer Part Number: DS1487N
• Description: Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver
• Manufacturer: NSC [National Semiconductor]

www.national.com
Applications Information
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.
(Continued)
6
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