I would consider circuit B as you have shown the use of the RO pins. Howeve= r, I would recommend additionally adding a 10k resistor on each RE* pin as = a pull-up to vcc. This will ensure that the two RO pins remain in high imp= edance state during power up. Sent from AOL Mobile Mail -----Original Message----- From: Jim Ruxton To: Microcontroller discussion list - Public. Sent: Sat, Mar 10, 2018 11:42 AM Subject: [EE] Routing 1 of 2 RS-485 inputs to 1 output Just curious how others might handle this scenario. I have 2 RS-485=20 signals. I want to route one of the 2 to a UART pin on a PIC. I am=20 looking at using 2 MAX485 receivers or something similar. These have RX=20 enable pins that either output the signal or put the output pin into a=20 high impedance state. I am wondering about tieing the 2 outputs together=20 and be sure I only have 1 of the 2 outputs enabled. I am just concerned =20 that on power up the outputs may not be in a high impedance state and=20 will fight each other until my PIC is fired up completely. My other=20 option is to join the 2 outputs with series resistors. Since I am going=20 to have a single optical isolator after the MAX485s I could tie the=20 outputs together through current limiting resistors going to the=20 isolator. Or maybe someone has a better suggestion or knows another=20 rs-485 IC that does this ie. allows the selection of 1 of multiple=20 inputs. I did a quick mockup of the 2 scenarios only showing the=20 relevant bits. I am considering here.=20 https://drive.google.com/open?id=3D1im2HMS2sjCmgZup= 1q0AzfC9YSY-Z1ew2 I would appreciate any thoughts or opinions. Jim --=20 http:/= /www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .