LUM0024AB Rev A
Chapter 10: Additional Transceiver
Information
This chapter contains additional information about the transceivers described in this manual:
l Operational RS422 and RS485 information
l Connector pin assignments
l Specifications
l Factory default settings
Operational RS422 and RS485 Information
For RS422 and RS485, the FreeWave transceiver can drive 32 standard unit loads and loads the bus with
only 1/8 unit load. This means you can tie up to 256 devices on the bus if all of the line receivers have 1/8 unit
load.
RS422 is used for 4-wire or full duplex communication with one Gateway and multiple Endpoints. The
FreeWave Master transceiver keeps the line driver asserted at all times. The maximum line length is 4,000
feet using two, 120 ohm twisted pair cables with a fifth wire for data common.
RS485 full duplex using 4-wire plus common is the same as RS422, except the system can have multiple
Masters on the bus.
The most common operation of RS485 is a two-wire comprised of a 120 ohm impedance single twisted pair. In
this system the loading of the FreeWave transceiver is as described above which allows up to 256 1/8 unit
load units on the bus. Maximum line length is also 4,000 feet with a third wire required for data common. The
FreeWave transceiver checks the line to be certain no other device is transmitting before enabling the line
driver for data transmission.
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