JP4 on pixie controllers

[Lights on Mandan]

I have seen it mentioned that you should put a jumper on JP4 in the last controller in a line.  Is this a requirement, or a recommendation?  What purpose does it serve?

I am trying to understand how the controllers process the signals and why we need to identify the last controller in a line.

Thank you to all the people who know FAR more than I do, for helping out the ignorant one.

 

[k6ccc]

The RS-485 specification includes a 120 ohm termination at both ends of the network.  The LOR USB adapter provides the termination at that end, and your SHOULD terminate the far end.  Some (most newer ones) have a selectable termination on the board controlled by a jumper or switch.  JP4 provides that termination.  You can also plug in a termination plug into the unused RJ-45 jack on the last controller.  I've built a bunch of those.

With that said, does it NEED to be there?  It depends.  How long is your network, how many controllers are on the network, and what data speed are you using?  Longer, more devices, and faster speed all make the need greater.  When LOR networks were generally running at 56 or 115 K speeds, it was fairly non-critical, but with pixels, the faster speeds are almost required.  So yes, use the termination.  Without the termination, the possibilities of data errors increases.

 

[Lights on Mandan]

Thank you.  This is making a little more sense to me (the uneducated) now.  JP4 jumpers on the last controller on each of my networks!

 

[TheDucks]

Just a heads up: Always refer to the manual for your model / version

JP4 (the termination) is only available on Gen 2 Pixies.  The Termination may have a different # or enable method on future models.

None of the CTB series up to Gen 3 have a built in Termination. @k6ccc method is the only way if that is the last unit.

The wattage is not important.  Amazon has these $6 per HUNDRED. All you need is the last 4" of good end  of an old CAT5 cable (we all have had one break the lock tine at one time or the other)

The resistor is connected across the Blue pair (4-5)

 

 

 

[k6ccc]

2 hours ago, TheDucks said:

The wattage is not important.  Amazon has these $6 per HUNDRED. All you need is the last 4" of good end  of an old CAT5 cable (we all have had one break the lock tine at one time or the other)

The resistor is connected across the Blue pair (4-5)

Actually the way I do it is to use a 1/8 watt 120 ohm resister, and bend the wire on one end over so now both wires point the same direction.  On the wire that is now passing the resistor body, slide either some very small heat shrink tubing or even the insulation slid off a small wire.  Then slide the two wires into the appropriate slots in the RJ-45 plug and crimp it.  If you really want to be fancy, before you crimp it, slide another larger piece of heat shrink tubing or jacket from a piece of Cat-5 cable over the resistor and wires so that when you crimp it, that is held in position and covers the resistor.  Note, you have to use a 1/8 watt resistor in order for the wires to be small enough to fit.