Post by thread:[EE]: 120 feet bidirectional commnucation

Hi to all, Soon my electronic gate will be ready witch is About 120 feet far from my desk and I need to Build bidirectional communication with whole House there are doors and switches I need to know The status of it. My favorite interface is I2C but the problem Is that I2C is not good for 120 feet distance I guess my Choice is RS485 differential phase but what I do not know is By using 4 wires 2 for receive and 2 for transmit can I communicate with all 35 sensors ?. So rs485 works like rs232 I do not see any way of sharing from same bus I need to make communication like I2c but for 120 feet long any help will highly appreciated. Andre -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

If you use 4 wires it is RS422. RS485 uses 2 wires, but you can only communicate in one direction at a time. For your use I think RS485 (2 wires) should work fine as long as you have one master and a number of slaves. The slaves only speak when spoken to by the master. If the master wants to know if the gate is open, it asks. Basically the master polls every slave periodically to see if they have info. But the master can issue commands any time he wants as long as a slave is not replying to his previous command. Sherpa Doug > {Original Message removed}

You can run RS485 with 4-wires for full duplex operation. Best Regards David Huisman ----------------------------------------------------------------------- ORBIT COMMUNICATIONS Reliable Wireless Solutions (Telemetry, Control, Monitoring ...) Website : http://www.orbitcoms.com PO Box 3469 Tuggerah NSW 2259, AUSTRALIA Phone: 61-2-4393-3627 Fax : 61-2-4393-3685 Mobile: 61-413-715-986 ----- Original Message ----- From: "Douglas Butler" <spam_OUTdbutlerTakeThisOuTIMETRIX.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Friday, February 22, 2002 8:26 AM Subject: Re: [EE]: 120 feet bidirectional commnucation {Quote hidden}> If you use 4 wires it is RS422. RS485 uses 2 wires, but you can only > communicate in one direction at a time. For your use I think RS485 (2 > wires) should work fine as long as you have one master and a number of > slaves. The slaves only speak when spoken to by the master. If the > master wants to know if the gate is open, it asks. Basically the master > polls every slave periodically to see if they have info. But the master > can issue commands any time he wants as long as a slave is not replying > to his previous command. > > Sherpa Doug > > > {Original Message removed}

Andre, You can attach multiple RS485 trancievers to the same RS485 bus. The trancievers go into a high impedence state when they are not transmitting. You probably can get by with RS485 (2 wires) rather than RS422 (4 wires) unless you really need full-duplex operation. See link below for a good reference document on RS485 and RS422: http://www.bb-elec.com/tech_articles/rs422_485_app_note/table_of_contents.asp Kirk > Hi to all, > > Soon my electronic gate will be ready witch is > About 120 feet far from my desk and I need to > Build bidirectional communication with whole > House there are doors and switches I need to know > The status of it. My favorite interface is I2C but the problem > Is that I2C is not good for 120 feet distance I guess my > Choice is RS485 differential phase but what I do not know is > By using 4 wires 2 for receive and 2 for transmit can I communicate > with all 35 sensors ?. So rs485 works like rs232 I do not see any way > of sharing from same bus I need to make communication like I2c but > for 120 feet long any help will highly appreciated. > > Andre __________________________________________________ Do You Yahoo!? Yahoo! Sports - Coverage of the 2002 Olympic Games http://sports.yahoo.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> Soon my electronic gate will be ready witch is > About 120 feet far from my desk and I need to > Build bidirectional communication with whole > House there are doors and switches I need to know > The status of it. My favorite interface is I2C but the problem > Is that I2C is not good for 120 feet distance I guess my > Choice is RS485 differential phase but what I do not know is > By using 4 wires 2 for receive and 2 for transmit can I communicate > with all 35 sensors ?. So rs485 works like rs232 I do not see any way > of sharing from same bus I need to make communication like I2c but > for 120 feet long any help will highly appreciated. RS-485 is an electrical spec only and leaves a lot to the individual implementation. Typically you use the differential lines to carry *one* half-duplex signal. All the transmitters on the bus cooperate using a higher level protocol to decide which one of them is allowed to transmit at a time. Another common implementation is to run two differential pairs when there is a "main controller". The main controller is always the sender on one pair, and different slaves respond on the other pair as the main controller asks them to. This scheme maps well to hardware UARTs because the send and receive for each unit on the bus can be hard wired to one of the pairs. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Sherpa, Thanks for your replay, I have max1482 chips that I can use. A few things are not clear for me lets assume I got 30 slaves and 1 master if 2 slaves try to Communicate with master at the same time then what will happen? I2C is kind of different it will wait until the bus gets free Do you know there rs485 mostly are used ? is there any chip to make I2C work for long distance ? Thanks again Andre >>>>>>>>>>>>>>>>>>>>> If you use 4 wires it is RS422. RS485 uses 2 wires, but you can only communicate in one direction at a time. For your use I think RS485 (2 wires) should work fine as long as you have one master and a number of slaves. The slaves only speak when spoken to by the master. If the master wants to know if the gate is open, it asks. Basically the master polls every slave periodically to see if they have info. But the master can issue commands any time he wants as long as a slave is not replying to his previous command. Sherpa Doug > {Original Message removed}

On Fri, Feb 22, 2002 at 10:31:32PM -0800, andre abelian wrote: > Sherpa, > > Thanks for your replay, > I have max1482 chips that I can use. > A few things are not clear for me lets assume > I got 30 slaves and 1 master if 2 slaves try to > Communicate with master at the same time then what will happen? That doesn't happen by definition. The primary node directs the secondaries as to when they may communicate. So if one secondary has been granted access to the line, the others will not communcate on that line until directed to do so. Also be very very aware that EIA485 (RS means recommended standard, EIA is a actual standard) doesn't have any data link layer, so any communications protocol you want to use you'll have to implement yourself. BAJ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> On Fri, Feb 22, 2002 at 10:31:32PM -0800, andre abelian wrote: > > Sherpa, > > > > Thanks for your replay, > > I have max1482 chips that I can use. > > A few things are not clear for me lets assume > > I got 30 slaves and 1 master if 2 slaves try to > > Communicate with master at the same time then what will happen? > > That doesn't happen by definition. The primary node directs the secondaries > as to when they may communicate. So if one secondary has been granted > access to the line, the others will not communcate on that line until directed > to do so. By who's definition? There is nothing in the RS-485 spec that prevents that. The spec says that multiple transmitters will not destroy each other by attempting to send at the same time, it does not say you can't do it. It's up to your implementation to watch out for that happening, usually by monitoring the output and comparing with the input, then retrying after a random delay, as in Ethernet collision detection or else by assigning a transmit window to each node. /\/\/\/*=Martin -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Fri, Feb 22, 2002 at 02:18:06PM -0500, Martin Peach wrote: {Quote hidden}> > On Fri, Feb 22, 2002 at 10:31:32PM -0800, andre abelian wrote: > > > Sherpa, > > > > > > Thanks for your replay, > > > I have max1482 chips that I can use. > > > A few things are not clear for me lets assume > > > I got 30 slaves and 1 master if 2 slaves try to > > > Communicate with master at the same time then what will happen? > > > > That doesn't happen by definition. The primary node directs the > secondaries > > as to when they may communicate. So if one secondary has been granted > > access to the line, the others will not communcate on that line until > directed > > to do so. > > By who's definition? There is nothing in the RS-485 spec that prevents that. > The spec says that multiple transmitters will not destroy each other by > attempting to send at the same time, it does not say you can't do it. It's > up to your implementation to watch out for that happening, usually by > monitoring the output and comparing with the input, then retrying after a > random delay, as in Ethernet collision detection or else by assigning a > transmit window to each node. That's why I included the second paragraph in my post. To quote: ----- Also be very very aware that EIA485 (RS means recommended standard, EIA is a actual standard) doesn't have any data link layer, so any communications protocol you want to use you'll have to implement yourself. ----- Since the primary/secondary relationship will have to be implemented in software, it can (and in fact must), enforce those rules. BAJ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> I got 30 slaves and 1 master if 2 slaves try to > Communicate with master at the same time then what will happen? This will cause a runaway nuclear reaction in the driver chips and all life as we know it will cease to exist. Seriously, the data will all be mush and none of it will get thru. You have to guarantee this won't happen with the higher levels of the protocol. For example, a slave only sends when requested to do so by the master, and the master makes sure only one slave at a time is supposed to send. You still have to deal with things screwing up and getting out of sync. I've done this on RS-485 by wrapping everything into checksummed packets, timeout rules, etc. I had such a system with an embedded Pentium master controlling 15 PIC slaves. Worked very nicely. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, .....olinKILLspam.....embedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hello Andre, Byron et all, Andre says: >>I2C is kind of different it will wait until the bus gets free >>Do you know there rs485 mostly are used ? is there any chip to make >>I2C work for long distance ? Byron says: > Also be very very aware that EIA485 (RS means recommended standard, EIA is > a actual standard) doesn't have any data link layer, so any communications > protocol you want to use you'll have to implement yourself. actually that means you *can* use I2C (or better, a variation of it) to implement long distance communication. It's not that dificult and requires 4 wires (plus ground) for the communication. Just use 75176's (or other 485 driver/receiver) to carry the I2C signals. The clock will always walk from the master to the slaves. The data line is bidirectional, so you'll have to tie the I2C-DATA signal on the PIC to the RX and TX pins on the 75176 and use another PIC pin to select 75176 TX/RX. Best regards, Brusque ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Researcher and Developer Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.