I need to deisgn a circuit to verify the connectivity (no open, no short) of eight data lines. I plan to use two I/O ports on one MCU, one port send data and another port receive data to do comparing. The same circuit will be used in another applicaiton case, 2-3 data lines will be fed with 35 Vdc from another device. To avoid damaging, the i/o ports of MCU need to be isolated. Is there any suggestion for the device for the isolation? If I want to use optocouplers (I/O -> optocouple -> optocouple -> I/O), how can I connect two coptocouplers together? Any suggestions are welcome.