Are both sides 0V connected together ? They don't need to be (depending on floating voltage levels) however you could try it. Or if they are, try disconnecting the common ??
You could try lowering the baud rate. The termination resistors are only required for long cable lenghts. If using term. resistors, ensure the cable impedance matches the resistors (i.e. use proper belden RS485 cable). Try using an alternative AC termination - i.e. a capacitor and resistor in series across A/B lines (can't remember values, see app. notes for the devices). Would be nice if you could see the data coming in both ends as to establish the actual problem. Kind regards, Darren Logan BSc(Hons) Development Engineer ------------------------------------------------------- Michell Instruments Ltd tel: +44(0)1223 434 854 Nuffield Close fax: +44(0)1223 434 895 Cambridge www.michell-instruments.com CB4 1SS mailto:[EMAIL PROTECTED] ISO9002 accredited: Q6284 * Member BCAS UKAS accredited: 0179 * Investor in People ---------------The dew point specialists-------------- This communication contains information which is confidential and may also be privileged. It is for the exclusive use of the intended recipient(s). If you are not the intended recipient(s), please note that any distribution, copying or use of this communication or the information in it is strictly prohibited. If you have received this communication in error, please notify the sender immediately and then destroy any copies of it. -----Original Message----- Sent: 19 September 2002 12:54 To: Multiple recipients of list CHIPDIR-L Hello Chipdir members, We are using LTC485 RS-485 transceivers and found some strange behavior. We have a test setup with two devices, one using a Sipex RS232/RS485 (selectable) transceiver in a industrial PC, and one of our own devices, using the LTC485. These two devices will only communicate if we remove the termination resistor of 120 ohm at one side, leaving the bus unterminated. When the resistor is placed, the voltage swing of the A and B channel is still about 2 Volt, which should be sufficient, according to the RS-485 documentation I have. Only differences below 200mV are undefined. However, the 2 Volt voltage is not enough to operate for some of the devices. We tried several LTC485's and found out that some of them worked fine with termination, but some didn't. Testcable length is an awsome 50 cm ;-) Any ideas or clues? Kind regards, Elbert Smit -- Author: Elbert Smit INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Author: Darren Logan INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
