Hostname Hardware New_ip kosu22.kosu 00A02416926D 139.78.122.129 All requests were successfully filled. ------------------------------------------------------- Thursday 7 /17/97 14:38 In message <199706181359.PAA08301@alef.ontonet.be>, Didier JEANJEAN writes: >The swing voltage is not 250mV. > >When we transmit a 1 the A is at 5V and the B is at ground. >When we transmit a 0 the A is at ground and the B is at 5V. >So the swing voltage is 10V. > >But for the receiver it is enough with a differentiel voltage accros A and >B of 250mV (this voltage depend of the chip) to detect a zero or a one >binary. The sign of this differential votage give the binary value (0 or >1). > >This give a really good distance also with poor wire. > >Didier > >---------- Hostname Hardware New_ip kosu22.kosu 00A02416926D 139.78.122.129 All requests were successfully filled. ------------------------------------------------------- Thursday 7 /17/97 14:38 >> From: Byron A Jeff >> To: PICLIST@MITVMA.MIT.EDU >> Subject: Re: 485 interface? >> Date: mardi 17 juin 1997 20:45 >> >> > >> > I have seen several references to interfaceing with a "485" network or >line. >> > So what the heck is "485" anyhow? I just haven't run across this before >so >> > a brief explanation and a pointer or two to some place to get more >would >> > be appreciated. >> >> RS-485 is a line protocol like EIA-232 (AKA RS-232). It uses differential >> signaling (two lines where each line must be of opposite polarity to >> signal a valid bit) with a very small voltage swing (250mv I believe). >> The differential signalling gives noise immunity while the small voltage >> swing allows for extremely high data rates (up to 10 Mbits/sec). In >addition >> RS-485 is designed for multiple drop operation. Up to 32 nodes can share >> a single RS-485 line and a single transmitter can multidrop message to >> multiple receivers at the same time. RS-485 is uni-directional unlike >EIA-232 >> so full duplex communication is not possible with a single RS-485 line. >> >> RS-485 has no provisions for flow control or collision >detection/resolution. >> So multiple talkers on the line at the same time will cause havoc. >> >> The transceivers for RS-485 are inexpensive and easily powered with just >> 5 volts. So special voltages are not required. >> >> Lastly the maximum distance on a single segment is 4000 ft. IIRC the 10 >Mbps >> speed cannot be sustained at that distance. >> >> >> As a line protocol it falls somewhere between EIA-232 and Ethernet. It's >> useful for multidrop networks. >> >> BAJ