RS-485 Data Bus
- Thread starter nov0798
- Start date
toymaster458
Active Member
If the only thing connected to the data bus is the keypad then the answer is yes to both. There can never be no more or less then 2 terminators on the data bus.OK, Im a little confused.If I have an M1G, and I only have one keypad, do I place the jumper on JP2 of the keypad, or on JP3 of the control board?
Thanks :
drozwood90
Senior Member
If it is RS-485, then you need TWO terminators. No more, no less.
The terminators are supposed to be at the ENDS of the bus.
In your case, your keypad is one end, and the main board is the other. So BOTH.
--Dan
Lagerhead
Active Member
Here is a good, though somewhat technical, paper on RS-485 that explains bus termination as well as cabling, topology, etc:
http://www.national.com/an/AN/AN-1057.pdf
http://www.national.com/an/AN/AN-1057.pdf
ddennerline
Active Member
I received one sporadic Keypad Error and started researching RS-485 bus errors. I searched the CT forums and read the Elk documentation to no end about RS-485 termination. I have an ElkM1G, M1DBH, and M1RF2G. Basically, I found out that RS-485 bus resistance was 179ohms without a black jumper placed on JP3 on control board. This value is out of tolerance. In small print on page 12 of installation, it say's:
Yes there was user error, but seeing how the M1DBH helps with home-run wiring, the instructions should be much clearer in my opinion - especially since the majority of installations I have seen on this forum use M1DBH. IMHO, the documentation should be more detailed as the 178ohm configuration appeared to be working correctly.
Example Instructions:
1) Make sure there are no J2/J3 jumpers on any keypad or expander board.
2) Make sure JP3 has a jumper
3) Check the RS-485 voltage
4) Check the RS-485 resistance without power enabled
5) Monitor the system diagnostics (using keypad) for small amount of time to ensure RS-485 bus is operating correctly.
With JP3 jumped, the resistance is 68ohms.
68ohms
M1DBH Socket 1 – Keypad
M1DBH Socket 2 – M1RF2G
M1DBH Socket3 – Terminating Plug
Black jumper on JP3 at control board
179ohms
M1DBH Socket 1 – Keypad
M1DBH Socket 2 – M1RF2G
M1DBH Socket3 – Terminating Plug
<no JP3 jumper which seems to be factory default>
Yes there was user error, but seeing how the M1DBH helps with home-run wiring, the instructions should be much clearer in my opinion - especially since the majority of installations I have seen on this forum use M1DBH. IMHO, the documentation should be more detailed as the 178ohm configuration appeared to be working correctly.
Example Instructions:
1) Make sure there are no J2/J3 jumpers on any keypad or expander board.
2) Make sure JP3 has a jumper
3) Check the RS-485 voltage
4) Check the RS-485 resistance without power enabled
5) Monitor the system diagnostics (using keypad) for small amount of time to ensure RS-485 bus is operating correctly.
With JP3 jumped, the resistance is 68ohms.
68ohms
M1DBH Socket 1 – Keypad
M1DBH Socket 2 – M1RF2G
M1DBH Socket3 – Terminating Plug
Black jumper on JP3 at control board
179ohms
M1DBH Socket 1 – Keypad
M1DBH Socket 2 – M1RF2G
M1DBH Socket3 – Terminating Plug
<no JP3 jumper which seems to be factory default>
felixrosbergen
Senior Member
So when using the DBH you need to set or change a jumper on the main board? Ive had a very occasional keypad issue.
Has anybody seen flashes of light coming of their keypads at odd time? Mine is in the bedroom and set to be very dim, but sometimes in the middle of the night it seems to light up briefly. It's hard to tell since it's so fast..it coudl be car headlights but i seriously doubt it.
Has anybody seen flashes of light coming of their keypads at odd time? Mine is in the bedroom and set to be very dim, but sometimes in the middle of the night it seems to light up briefly. It's hard to tell since it's so fast..it coudl be car headlights but i seriously doubt it.