Network Communications—N2 Communications Bus
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Troubleshooting Procedures
The N2 Bus is a reliable communications bus. However, there are
situations in which communication problems may occur. Under most
circumstances, you can detect a problem by examining the XMIT and
RECV LEDs on the N2 device. If they are not flickering, or are flickering
irregularly, the bus is not working properly. You may also refer to the
N2 Bus Statistics window under NC Diagnostics at the OWS. (Examine
the Number of Retries figure.)
The most likely problems with a malfunctioning N2 Bus are:
•
broken or frayed wire
•
improper bus termination
•
incorrectly set end-of-line switches or jumpers
•
improper channel switch selection
•
defective N2 device
•
too many N2 devices defined
•
N2 Bus is too long
•
N2 Bus has “T” or “Y” connections installed
•
ground loop present on N2 Bus
•
defective repeater
•
defective surge protector
•
communication terminal board failure
A few of these problems are detected with a Digital Voltmeter (DVM),
and you can use an oscilloscope to pinpoint communication faults over the
N2 Bus.
The wire used for the N2 Bus must be free of broken or frayed sections.
If any of the three signal lines is broken or frayed, the devices that are
located after the break will report offline. To check for the defective part
of the cable, start at the device that physically precedes the first offline
device. The problem is likely in the cable between the last online device
and the first offline device.
Overview
Checking for
Good Wire
Runs
