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RC7 isn't ttl buffered

 
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Calamar



Joined: 07 Sep 2003
Posts: 60
Location: Buenos Aires (Argentina)

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RC7 isn't ttl buffered
PostPosted: Sat Feb 11, 2006 4:40 pm     Reply with quote

I was sexpecting connect a max485
directly at my 18f452, but:

(18f452) VIH = 0.8x Vdd ( 5 * 0.8 = 4) (worst case)
(max485) VOH = 3.5V (again worst case)

There are another rs485 compatible with the pin RC7 ?
I mean a cheaper one and esay to get in the most electronics shops.

(I know that the configuration 18f452-max485 works anyway
but I'd like keep my system under specifications, the rs485
isn't critical feature but I'm afraid to use it
without a field experience)
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)
Ttelmah
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PostPosted: Sun Feb 12, 2006 3:14 am     Reply with quote

If you want to be sure, just add a pull up resistor.
In fact the MAX485, is 'in spec'. Look at the loadings for 'worst case'. This, is normally for 4mA drawn, when the input on the PIC, only draws uA. There is a graph given for Voh, and it will give the required 4v, at lower output currents.

Best Wishes
Humberto



Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata

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PostPosted: Sun Feb 12, 2006 10:23 am     Reply with quote

Quote:

There are another rs485 compatible with the pin RC7 ?


RS485 compatible means that the transceiver meet all the specifications established in the
EIA Standard. You can use 'any' RS485 transceiver, of course there are different 'flavors',
but this features are not concerned with the standard itself, the differences are the
adds-on upgrade features offered by the manufacturers like: power consumption,
allowable data rate, temperature failsafe, shutdown capabilities, ESD capabilities, etc.

I have a lot of applications deployed using RS485 transceivers + PIC and never get any
problem with this issue.


Humberto
Calamar



Joined: 07 Sep 2003
Posts: 60
Location: Buenos Aires (Argentina)

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PostPosted: Sun Feb 12, 2006 1:14 pm     Reply with quote

I value a lot both answers, thank you.
There are a high knowledge level
in the member of the list, I'd like know
if someone know another forum with
so high level like this about analog and
embedded design.
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)
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