AVR-Chat

Thanks for the reply. Right now I am stuck with 481 on the board, but it 
seems like it will meet my requirements. I've been reading some more 
about this throughout the day and it seems that having to bias the bus 
(using a pullup and pulldown) configuration is quite commonly done.

-jr

Lasse Madsen wrote:

> Hi James
>
> I have a suggestion for you not a solution to your particular problem.
>
> I’ve used RS485 for a long time and I’ve found the (more expensive) 
> auto bias self terminating IC’s from maxim to work perfectly where 
> others failed!
>
> /Regards
>
> Lasse M.
>
> -----Original Message-----
> *From:* James Russo [mailto:jr@halo3.net]
> *Sent**:* 1. oktober 2004 16:03
> *To:* AVR-Chat@yahoogroups.com
> *Subject:* [AVR-Chat] RS485 w/ MAX481, terminators not needed?
>
> Hello Everyone,
>
> I am working on getting two MAVRIC-II (Mega128) boards talking using
> RS485 (MAX481 to uart1). I am using a short segment of (<5feet) of 3
> twisted wires (A,B,Gnd). My problem is that with the terminators
> installed on either node, my data output from the RS481 is not high when
> the there is no driver active on the bus. This causes the uart to
> constantly see a start bit, and then return a 0 after every byte
> received. However, if I remove the terminators on both everything seems
> to work as expected.
>
> According to the spec sheet for the 481, the DO pin should be high when
> the "inputs are open"? I have a feeling it has to do with the very short
> RS485 run with just two nodes on it and the involved resistances, but
> hopefully someone else has more experience and can give me a pointer.
>
> Thanks,
>
> -james
>
>
>
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