Also check the manuals to item(s) you are connecting to. RS485 is normally a
multidrop system and may also require a terminator. GE PLC's use it and have
configurations in their online manuals.
RS485 is not well documented by most
vendors, as your ignorance plays into
their products sales goals quite nicely.
However, there are some very excellent
resources you can read about RS485. Then
you can 'jam-up' the vendor of choices
as to why their product(s) are so hard
to use. I avoid Windoz based gui crap,
that you'll discover later on, once
you master RS485......
Also, RS 485 can be redered( available)
on a product via hardware base, i.e.
it's in the chipset, or software, i.e.
its in the firmware, or a combination of
both. The best things is to discover how
the vendor implemented RS485 on their
product. Most vendors do not give up
this information, readily, because they
have done a shitty job in there RS485
offering(s). Once you figure out what
chipset they used to partical or fully
implement RS485, you 1/2 the way home to
reverse engineering their mess.
Circuit Cellar publish an article called
"RS-485 Netowrk for Embedded System" and
is a most excellent starting point.
Search out silicon vendors that offer
RS485 chipsets, is also and excellent
WE most often build our own boxes, i.e.
RS485 2 and 4 wire interfaces plus
microcontroller, and then get each and
every vendors RS485 device to work with
a box that we write assembler or ANSI C
on. If you only have a few devices that
need to talk RS485, then canned vendor
based products may work. If things do
not work then you have to build a
hardware based sniffer for RS485. When a
vendor (and this is rare) does offer a
built in RS485 sniffer, it was usually
develop by the same engineer (usually a
clueless EE that cannot code) that
integrated the RS485 device into the
We use a combination of EEs, Computer
Engineers and Mostly Computer Scientist
to develop software. Companies that
mostly use EEs to write software
specification and code, are usually
BEST of Luck!
James Horton, PE
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