Hi Elbert, The only reason I can see this happening is if you are exceeding the common-mode voltage of the receiver. Your interconnect cable should have wires and a shield or a ground wire. The grounds of the chips on both sides should be tied to the shield or ground of the cable. Since you are driving an card with the receiver already on it the connector you are plugging into should have +. -, and ground.
>-----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 -Bob -------------------------------------------------------------------- Robert Ritchey Quest Engineering & Development 1328 East Cottonwood Lane Phoenix, AZ 85048-4765 Tel: (480) 460-2652 FAX: (480) 460-2653 E-Mail: [EMAIL PROTECTED] E-Mail: [EMAIL PROTECTED] E-Mail: [EMAIL PROTECTED] E-Mail: [EMAIL PROTECTED] WWW: www.QuestEngDev.com/ WWW: www.Smart-Fly.com/ -------------------------------------------------------------------- -- Author: Robert Ritchey 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).
