RC7 isn't ttl buffered

Calamar · Posted: Sat Feb 11, 2006 4:40 pm

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 · Guest

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 · Posted: Sun Feb 12, 2006 10:23 am

Calamar · Posted: Sun Feb 12, 2006 1:14 pm

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)