Hi,
RS-485 devices are treated similarly to RS-232. There are a number of
serial classes that may be used. I have one in my book (see below) or you
can download NETComm.ocx from my homepage. There also are many other serial
objects available for free and several commercial ones that offer extended
features -- none of these additional features, such as error corrected file
transfers, should be needed by you.
The feature of RS-485 communications is that it often is half duplex. That
is, the communications channel is shared between multiple devices. To solve
the problem of sharing this channel, a communications protocol is needed.
The details of the communications protocol is proprietary. That is, it will
be developed for the specific system in question. You would use the
documentation provided by your device manufacturer to implement this in your
software. Usually, there are two phases. One of these allows the physical
sharing of the channel -- this often uses CTS and RTS to control. The
second is the command and response message structure that is used for
sending and receiving data.
I have a more detailed explanation in my book. See below.
Dick
--
Richard Grier (Microsoft Visual Basic MVP)
See
www.hardandsoftware.net for contact information.
Author of Visual Basic Programmer's Guide to Serial Communications, 4th
Edition ISBN 1-890422-28-2 (391 pages) published July 2004. See
www.mabry.com/vbpgser4 to order.
