ABB EQmatic
Planning and application
QA/S x.yy.1 | 2CDC512090D0202 103
Troubleshooting RS-485
To minimize potential sources of faults, a few basic aspects should be taken into account on the
usage of RS-485.
Determine the communication characteristics of a device before the system design is completed. Pay
attention to the following points here:
• Two-wire or four-wire system
RS-485 systems can be either two-wire or four-wire systems. The two-wire configuration - with
the additional earth wire - reduces the wiring costs, however it is limited to half duplex
communication (cannot receive and transmit at the same time). The majority of RS-485 devices
have two-wire configurations.
• How high is the response time of the device (processing time)?
• What is the address range of the device that can be programmed?
• Which speed is supported?
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