AVR-Chat

>   Note that for short RS485 runs using these chips, I've
> found that the terminator is generally unnecessary.

My situation is that with the terminators on, it doesn't keep the RO 
high. With them off it does. I have put pull-up/pull-down resistors and 
activated the terminators and all seems well.

Seems like according to the datasheet this wouldn't be necessary. Page 
10 of the data sheet (the table on the right) shows that the RO should 
be "1" when the inputs are open. What would be the electrical definition 
of "inputs open" be?

> Thus, when no driver is driving the bus, the state should not
> fluctuate.  

Fluctuating would be worse then saying logic low (start bit) with no 
xmiter. I am not seeing that, I am only seeing after turning off the 
driver on one node, the other node is recieving a 0.

> Even so, supplying the pull-up / pull-down resistors on
> the A/B lines might be a good idea and is pretty common in RS485
> implementations, especially since you might not be able to guarantee
> that every transceiver on the bus has this feature.

So, I would think that using these two boards together, I shouldn't need 
the pullup/down since it has this "fail-safe" feature. It's kind of a 
non-issue for now since I will just use the pull-up/pull down, but would 
just like to know why chip isn't working as advertised, even if only for 
my own enlightment.

take care,

-jr