Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 15
With the EOL jumpers set to the In position, a positive bias voltage is
applied across the N2+ and N2– lines. This bias voltage is referenced to
the REF line. The bias resistors and the 220 ohm termination resistors
combine to form a voltage divider. By taking the tolerances on the
resistors and the power supply variations into account, you should expect
to see the following voltage levels on the N2 lines (MM-CVT101 is
disconnected from the PC but still connected to the N2 Bus):
Voltage from N2+ to N2– = +0.36 to 0.92 VDC*
(DMM+ probe on N2+ terminal; DMM- probe on N2– terminal.)
Voltage from N2+ to REF = +2.45 to 2.98 VDC
(DMM+ probe on N2+ terminal; DMM- probe on REF terminal.)
Voltage from N2– to REF = +2.06 to 2.54 VDC
(DMM+ probe on N2– terminal; DMM- probe on REF terminal.)
*If the difference from N2+ to N2– is greater than 0.36 V, your system
should be able to communicate.
If communication is taking place, voltage on the N2 Bus fluctuates and
therefore the DMM will read these fluctuating voltages. An oscilloscope
provides a more accurate reading.
Setting the EOL terminations correctly on the devices connected to the
N2 Bus is crucial to proper and reliable communication. Follow these rules:
1.
Always set the EOL jumpers to In for the Companion PC or
Panel/LTD. This device is always set as end-of-line because all the
controllers on the N2, namely the ASCs, are self-terminating (they do
not have EOL jumpers). Note that, as in Figure 8, the Companion PC
or Panel/LTD does not necessarily have to be at the end of line.
2.
If possible, terminate the two devices that are at the far ends of the
N2 Bus. If one of these devices is self-terminating, terminate the
other, which will have an end-of-line jumper. In many cases, this will
be the MM-CVT101, Companion Panel/LTD, or repeater.
3.
If only one device on the bus can be terminated, jumper it as an
end-of-line device.
During commissioning, visually check the N2 EOL jumpers at the
Companion PC or Panel/LTD.
●
For the Panel/LTD version, the end-of-line jumpers are located on the
Panel’s circuit board (W2 and W4).
●
For the PC version, the jumpers are located on the MM-CVT101
(W1 and W2).
●
For the repeater, the jumpers are found under the top cover.
Proper EOL
Settings
Summary of Contents for METASYS ASC
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