[aprssig] RS232,TTL and RS422 interfacing

[KF4LVZ]

On 2016-07-05 11:32, Robert Bruninga via aprssig wrote:
> Here is a nice document that shows all the ways to do simple connections between 
> all the serial standards, TTL, 232, 422, etc.
> 
> I just put it in my “how-to” folder:
> 
> http://www.ti.com/lit/an/snla041a/snla041a.pdf
> 
> Bob, WB4APR
> 

The document covers unidirectional signal levels and level shifting but
it doesn't cover bi-directional applications.  RS485 is half duplex
using the same twisted pair for transmit and receive.  You have to add
additional switching logic to convert TTL/RS232/RS422 full duplex
signals to RS485 half duplex without accidental echos (or have the
software deal with the echos).