184 Ethernet module User’s Manual
Chapter 8 Error Handling
8
The ACC LED indicates when the S controller is accessing the EN311 and the 
EXT.POWER LED indicates when 12-VDC power is supplied to the MAU power supply 
terminals.
Table 8-3  States Indicated by the ACC and EXT.POWER LEDs
LED display Description
ACC(Access) Indicates whether or not the S controller is accessing the module.
• On ••• The S controller is accessing the module.
• Off ••• The S controller is not accessing the module.
• On after EN311 initialization completes when power is first 
applied. (Access starts.)
If this LED does not turn on after power is turned on:
1) First, verify that the S controller and the EN311 are correctly 
connected to the base unit. Then:
Check the modules by
2) Combining the EN311 with a different S controller.
3) Combining the S controller with a different EN311.
If this LED does not turn on at step 2 above, then the EN311 itself 
is defective. Replace the EN311.
If this LED (in the alternate EN311) does not turn on at step 3 
above, then the S controller firmware does not support the EN311 
or the S controller itself is defective. If the S controller is defective 
replace it.
Supplement:
We recommend keeping spares on hand to minimize the time 
required determining the location of the fault using the above 
procedure and to minimize the time required for recovery.
EXT.POWER
(External power)
Indicates whether or not 12-VDC power is supplied to the 
MAU power supply terminals.
• On ••• 12-V power is supplied normally.
• Off ••• 12-V power is either not supplied, or is abnormal.
• If the S controller side power is not turned on, this LED will not 
light.
If this LED does not turn on even if the S controller power is 
turned on, check:
1) whether or not the external power supply is operating correctly
2) whether or not the external power supply is connected with reverse 
polarity.
Replace the module if neither of the above caused the 
problem.