Ed Jiang

AN1857 RS232 optoisolation interface

Discussion created by Ed Jiang on Mar 26, 2013
Latest reply on Mar 27, 2013 by Ed Jiang



I built a Hardware connection for MC9S08MP16, which is the same as described in app note AN1857, page 13. I try to communicate using Freemaster, with correct Baud rate setting. Unfortunately, it doesn't work. When I use P&E micro debugger, the communication is fine.


I measured my PC and found both pin 4 and pin 7 is of voltage around -11V. Anyone has an idea about this configuration?