Is there a standard naming convention for RS-485 terminals?  It looks like
I've worked myself into a corner by adding bias resistors to a design.
I've read the Bob Perrin article from Circuit Cellar Ink ("The Art and
Science of RS-485"), National app note AN-847 ("FAILSAFE Biasing of
Differential Buses"), and the B&B Electronics RS-485 app notebook.  To my
eye, all three imply that a pullup to positive supply is used on the
non-inverting input, and a pulldown to ground is used on the inverting input.

So far, so good.  The Perrin and B&B text both refer to the inverting
terminals as 'A', and the non-inverting terminals as 'B'.  I've got
hardware with pullups on 'B', pulldowns on 'A'.  But wait--it starts to get
interesting...the datasheets for the MAX485, AD485, and LTC485 all have the
inverting input labelled as 'B'!  Argh.

Can anyone shed some light on what the proper bias configuration should be?
 How about the terminal naming convention--is A inverting or non-inverting?


newell

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