All - I noticed that you didn't get the screen shot attachment....probably too big - try this one. Jim -----Original Message----- From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx] Sent: Wednesday, June 12, 2002 8:14 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] rs-485 reflection problem Hello all - I have an RS-485 multipoint system with the fail-safe biasing at one end and a 120 ohm resistor at the other end of a 15 foot twisted pair interconnect. (the fail-safe circuit is : Vcc->536ohm<->130ohm<->536ohm->gnd). Since I have a multipoint system, the RS485's must tri-state (duh). When the rs485 driver at the failsafe end goes from a "1" to tristate, the high end trickles down to the failsafe bias point, but the low end 'slams' up close to the high end and then trickles down with the high end to the bias point. I've attached a screen shot of this (note: you will not see the below problem in the screen shot, but you do see the slam). Now to my problem : when this low end slams up, it is sending a non-differential wave down the t-line all the way to the end, where it reflects ABOVE the high point and causes a 60ns glitch at the single-ended output of the 485 receiver - and that is a bummer. Any suggestions for a fix? regards, jim peterson -- Binary/unsupported file stripped by Ecartis -- -- Type: image/bmp -- File: 485_hiz.bmp ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu -- Binary/unsupported file stripped by Ecartis -- -- Type: image/bmp -- File: 485_hiz.bmp ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu