Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 113)

Publication DNET-UM072C-EN-P - July 2004
Correct and Prevent Network Problems 5-9
Table 5.2 lists nominal voltage readings.
If voltages are too low
If the CAN_H to V- and CAN_L to V- voltages are too low (less than 2.5V dc
and 2.0V dc, respectively), the transceiver or wiring may be bad.
To check the transceiver for proper operation:
1. Remove one DeviceNet node from the network.
2. Use an ohmmeter to check for resistance greater than 1M Ω between:
• V+ and CAN_HI
• V+ and CAN_LO
• V- and CAN_HI
• V- and CAN_LO
TIP
Because the differential voltages are constantly shifting
among the three wires, the voltages on your scope trace
may differ from the nominal voltages shown in Table 5.2.
These voltages assume no common mode effect on the V-
and are for reference only.
Table 5.2 Nominal DeviceNet voltage readings
when a network master CAN_H to V- voltage
should read CAN_L to V- voltage
should read
is not connected to the network between 2.5 - 3.0V dc between 2.5 - 3.0V dc
is connected to, and is polling
the network approximately 3.2V dc approximately 2.4V dc