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Elk M1 RS-485 wiring?


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#1 bucko

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Posted 25 July 2018 - 06:00 PM

My LAN is 569B. Using an M1, M1DBH, M1KYPD2 (2), expanders, serial to RE-485, Output expanders, etc. Total 7 devices plugged into the M1DBH.

All my M1 devices terminate to the M1Dbh as 568B, Just like my LAN.

 

System up and running 5+ years, but always experience comm delays using the F buttons on the KYPD's. I see where Elk says they should be wired 568A. Could this be the source of my comm delays? Should I re-wire to 568A everything that is internal to the Elk panel?

 

Of course the XEP to my LAN would be 568B, but all else 568A?

 

What do you all think?



#2 RAL

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Posted 25 July 2018 - 07:20 PM

With a CATx cable used for ethernet, it doesn't matter whether the connectors are wired using 568A or 568B, as long as both ends are the same (unless you want a cross over cable). You can even connect a 568A cable to a 568B cable to make a longer cable if you need to.
 
The difference between the A and B wiring is that the pin positions of the orange and green pairs are swapped.  The DBH uses these pairs to form the daisy chain from one device to the next.  Off the top of my head, I can't tell you which pair connects to the previous device in the daisy chain and which pair is used to connect to the next.  But it really doesn't matter - the wire pairs are connected together at the keypad or other device anyway.  And the electrons don't care what color wire they are traveling on.
 
I'm not sure what would be causing the delay with your F-keys.  But I don't think it has anything to do with using 568A vs 568B.

Edited by RAL, 25 July 2018 - 07:22 PM.


#3 bucko

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Posted 26 July 2018 - 01:05 AM

I understand the diff in the two. But the Elk is a different animal. Most of the Elk  RS-485 devices are terminal connections at one end, and a RJ-45 at the other to the DBH. Therefore if Elk says it must be wired 568A, and  wired it 568B, I would assume that this could indeed be a problem. 
 
That is the point of my question.

Edited by bucko, 26 July 2018 - 01:08 AM.


#4 RAL

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Posted 26 July 2018 - 03:53 PM

If you are using the DBH and RJ45 connectors, then there should be no terminators on any of the devices plugged into the DBH.  The only terminator would be plugged into the next unused jack on the DBH.

 

Perhaps the picture below will help to show why either a 568A or 568B cable can be used.

 

The picture shows the wiring for just one wire of the green and orange pairs.  These pairs carry the Data A and Data B signals. The first device is connected to the M1DBH with a 568A cable, while the second device is connected with a 568B cable.   With 568A, the green wire connects to pin 2 of the RJ45 plug, and the orange wire connects to pin 6.  With 568B, this is reversed.   But since the orange and green wires are connected together at the other end of the cable where it connects to the keypad or other device, either type of cable will work. It doesn't matter which color wire goes to which of the two pins.

 

The only place where using the 568A pin assignments matters is at the terminator plug.  The terminating resistor needs to connect to the incoming signal pins in the RJ45.  Thus, the resistor connects to pins 6 and 3 of the RJ45 (the orange/white and white/orange pair).  Unless you are constructing your own terminator plugs rather than using the one supplied by Elk, you shouldn't have to worry about this.

 

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#5 bucko

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Posted 26 July 2018 - 05:24 PM

Thanks RAL. That makes sense to me. I will leave my wiring as is and look at something else causing my comm issues. Time to break out my meter and see if I find a device/s terminated elsewhere than the DBH.



#6 mikefamig

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Posted 27 July 2018 - 07:15 AM

A quick way to tell if you have the data bus properly terminated is to turn off all power to the system and connect an ohm meter to the M1 panel with one lead on the DATA A connector and the other lead on the DATA B connector. You should measure 65 ohms +-10 ohms.

 

Mike.



#7 bucko

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Posted 27 July 2018 - 09:57 AM

Bus is all good. I got 67 ohms and clean VDC to all devices. Brad is trying to help out on this as well. 

I will report how it all goes as soon as I find a solution.






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