The less than simple answer is that RS-485 has a much better common mode rejection ratio. If one observes the same signal in both transmission wires, the error can be corrected very easily. Since RS-485 carries both wires as signal wires with some impedance, the common-mode noise can be eliminated. This is true for RS-232, but to a much lesser extent since the ground side of the common mode signal will usually be substantially less than the signal side. -----Original Message----- From: Montaigne, Mike To: PICLIST@MITVMA.MIT.EDU Date: Thursday, November 06, 1997 10:14 AM Subject: Re: [OT}balanced line >The simple answer is that the noise cancels out. I believe the >impedance of the line is a lot lower also - around 120 ohms for 485 and >2K for 232. Any external noise will be equally induced in the same >polarity in both the 'true' and 'not-true' signals. The lower the >impedance of the line, the harder it is to induce a noise signal to it. >Same principal for low z balanced microphones. Another example is your >telephone. Lots of unshielded wire running throughout your house and >yet not much hum. Does this help? > >>---------- >>From: Frans Gunawan[SMTP:f@POBOXES.COM] >>Sent: Thursday, November 06, 1997 6:02 AM >>To: PICLIST@MITVMA.MIT.EDU >>Subject: [OT}balanced line >> >>I would like to ask, why with using balanced line(rs485) data can be >>transmitted longer than using unbalanced line(rs232)? >>I can't find good explanation about this. if possible, detail please... >>thanks >>www.poboxes.com/f >>f >>