What indication will appear in case of one of A320 LGCIU is inoperative?
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A320 ECAM "WHEEL" page

The answer:
The LGCIUs (landing gear control and interface unit) receive position information from the landing gear, cargo doors, and landing flap systems and process gear and door position, sequencing, control, and gear lever selection. 

When one of two LGCIU is inoperative (№6) amber XXXs in the triangle - indicates that one LGCIU has failed.

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Source: http://www.a320dp.com/A320_DP/landing-gear/sys-12.2.0.html