If you are real clever and want to add a small cap and a couple of
transistors I bet you could do the entire interface with 1 PIC pin.
Given that the slew rate on the pic TX pin is known.




On Thu, 8 Jul 1999, John Esposito wrote:

> Question:
>
> I am trying to implement RS485 using a Maxim 3082 (half duplex) and a PIC.  I
> want to conserve PIC I/O pins (don't we all??); is this layout acceptable?
>
> PIC RB0 - controls TX/RX mode; tied directly to MAX ~RE (rx enable not) and MA
X
> DE (tx driver enable)
> PIC RB1 - bi-directional input; tied directly to MAX RO (rx output) and MAX DI
> (tx input)
>
> When RB0 is low (receiving), RO splits its output between DI (which is in don'
t
> care state) and RB1
> When RB0 is high (trans), RB1 splits its output between DI and RO (which is in
> High-Z)
>
> Is this acceptable?  Is any other hardware (resistors, etc) necessary?  Assumi
ng
> I allow for propagation delays, all should be well, right??
>
> Any comments are greatly appreciated.
>
>
> Regards,
>
> --John
>