Dear All,
I am newbie for this forum.
Based up on the DIP switch selection our circuit will give output as RS232 or RS 485.The maximum data transfer rate will be 115 kbps.
We have connected the bidirectional tranzorb across each data line.(RS232/RS485)
We want to use the common surge protection techniques for both the modes(RS232/485).
As per my understandings, shall I connect the ISOLATED GROUND in the highlighted section?(Refer attachment –CKT_highlighted)
After doing this correction, whether this protection circuit will work for both the modes without any problem?
Should we need to perform some other modification?
Kindly give your valuable comments.

Thanks & regards,
S.Saravanakumar

 

I rarely get involved with serial data transmission but I do know that common mode suppression is far more effective than some might think. There are also cases where you need to do the reverse of common mode but I forgot the term for that.

I did however run into this web page which may be of some interest. Chances are it's stuff you already know anyway but there could be something in there that might trigger an idea:

http://www.bb-elec.com/tech_articles/rs422_485_app_note/transient_protection.asp