At 09:52 9/07/99 -0400, you wrote:
>Dennis:
>
>The MAX3082 is half duplex - does this change what you described?
>
>
>
>Yes this could be a bit messey in that the chip you want to use is full
>duplex. There will be some small amounts of backdrivig when changing from
>TX to RX and Vice versa. But most of this will be on the RS485 line, thus
>you may get some small glitches when chanigng state, unless you force an
>idle state at both ends before attempting to start a transmit cycle.
>To avoild contention at the PIC on the data line, when changing from
>Transmit to receive mode, set it to an input, then change the enable line
>to the RS485 driver, also you will need to pull this data line (On the PIC
>side) to the idle state so that during this process you will not cause crap
>to go out (Resistor required).
>When going from RX to TX ,set the data line to an output first (An place in
>the idle state) then change the driver enable. The small contention time
>can be lived with, if you want a resistor say 1k can be in series to reduce
>the current flow at this point in time.
>Repeat the same process on the other end. Dont forget to terminate at
>100-120R on the 485 side. You may also need to bias the lines so that the
>idle state is guarenteed at all times when nothing is connected etc.
>
>Dennis
>
>

I will have to look at teh MAX data to see if that is so. The MAX may have
internal resistors. Whatever the results, I think that the basic control
remains the same.


Dennis