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When purchasing devices for an RS-485
system many pitfalls can be avoided by determining the device's
communications characteristics before the system design is
complete. Knowing what questions to ask up front can save
a lot of troubleshooting in the field. The following device
characteristics are all things that should be answered in
the system design stage.
- Is the device configured for two-wire
or four-wire systems?
- Is a signal ground connection available?
- Is the device isolated? Does it contain
surge suppression?
- What value bias resistors (if any)
are used in the device? Are they accessible for modification?
- Is the device terminated? Is it accessible
for modification?
- What is the device's response time
(turn around delay)?
- What is the programmable address
range of the device?
- What baud rate, or range of baud
rates, is supported?
If possible it is often useful to have
a schematic of the serial port of each device in a system.
The schematic can provide additional information that may
be useful in troubleshooting or repairing any problems in
the data system.
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