Installing keypad, rs485 termination questions

[n8huntsman]

I fully understand terminating rs-485 data lines but Im confused by the wording in the M1KP3 manual.

 

"The last device on each cable MUST have a terminating resistor installed (activated) via the 2 pin header/jumpers marked JP1 on M1KP2 Keypad and expanders, JP1 on M1KP Keypads."

 

1.) Maybe just nit-picking the English but that wording seems odd since they're apparently labeled JP1 on expanders, M1KP2 and M1KP?  I only raise the question because I wouldnt be surprised if it's just me reading it wrong or missing something.

 

Next, "Place a black shorting cap from hardware pack onto the 2 pins to install a 120 Ohm resistor across data lines A & B."

 

2.) Does the shorting cap (jumper) automatically add 120 Ohm resistance or do I need to somehow add the included resistor with jumper on JP1?  Used plenty of jumpers but never in conjunction with a resistor.  See my confusion on that one?  If they hadn't included a resistor I probably would have assumed there is a resistor on the board that is jumpered in when placing the jumper on JP1 but because of the inclusion of the resistor I'm second guessing myself.

 

Lastly, "The RS485 Data Bus must NEVER have more that two (2) terminating resistors header/jumpers installed."

 

3.) Again, I can read this multiple ways but I assume this means that since there is one terminator per branch, you can have a maximum of two branches.  I can think of why you would ever have two terminators on a single branch so Im pretty sure that's not what they are saying.

 

Probably overthinking it but I don't want to ruin a brand new panel so I'm asking.

Thanks

[n8huntsman]

NM on #2 which was my most important.  I checked with my DMM and saw that with the jumper on, it reduced resistance across the data lines to120Ω, which is correct per the manual.  Then after looking at the included resistor closer realized that it was a 2.2kΩ eol.

 

Also found in the M1 manual it is a little more clear, although incorrect, "Jumpers are marked JP2 on keypads, JP1 on Expanders. Control

Hardware pack has two black jumpers for this purpose. Jumpers engage a 120 Ohm resistor across data A & B lines."  My keypad, the newer M1KP3, does not have a JP2, but at least I can tell where the mistake in the manual occurred.  

[n8huntsman]

Last question.  I'm using old existing wiring, not CAT5.  It's regular old 24-6.  There are two homeruns that were originally pulled for keypads.  Since I can apparently only have two branches and I will most likely need more keypads in the future, can I use the two extra wires at keypad #1 to "return" the two data wires over homerun #1 to the panel, connect them in the box (not to the panel) to the data wires of homerun #2 which will run to keypad #2 and terminate them there.  This will make the data wire length 4 times longer but will still be well within 400'.  The distances are short, but the data length will be much longer than the ground and power for #2.  Not sure if that would cause and issue.

If you need me to draw a picture let me know.  It sounds confusing when I type it.

[blueman2]

Last question.  I'm using old existing wiring, not CAT5.  It's regular old 24-6.  There are two homeruns that were originally pulled for keypads.  Since I can apparently only have two branches and I will most likely need more keypads in the future, can I use the two extra wires at keypad #1 to "return" the two data wires over homerun #1 to the panel, connect them in the box (not to the panel) to the data wires of homerun #2 which will run to keypad #2 and terminate them there.  This will make the data wire length 4 times longer but will still be well within 400'.  The distances are short, but the data length will be much longer than the ground and power for #2.  Not sure if that would cause and issue.

If you need me to draw a picture let me know.  It sounds confusing when I type it.

 

Well, this is one I can answer!  Yes, you can do a return run for the data using the other 2 wires.  No need to return the power/GND.  I have done this several times when I wanted to use the other 2 wires of an 8-wire cat 5 to bring the I/O connections back to my main closet.