TCAS is the Interrogator, not the Reporter
This is misleading: "if u have TCAS, just select the mode XNDR or ALTOFF NOT TA/RA.
It is especially important during low vis weather,so controller can track your progress.TARA only when entering runway in use.It is nerve recking to see alt reporting of an aircraft taxiing on // taxiway when you are taking off in low vis conditions."
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The transponder is the only device replying to TCAS, or replying to ATC SSR. If the Mode S transponder (required with TCAS) is reporting ON Ground, its replies will be ignored by TCAS interrogators in the area.
If the transponder is reporting altitude within 180 feet of runway elevation, as in a Mode C reply, it will likewise be ignored by TCAS in other aircraft. Do not turn off ALT replies (ALT OFF) on your ATC/TCAS control panel unless ordered by ATC, or your transponder will reply with no altitude, maybe causing false TA alerts to other aircraft. (The false alert part depends on the ON Ground priority in the calculations, which may not be consistent between TCAS and transponder manufacturers.)
TCAS coordination between planes is via the transponders. Your TCAS interrogates the other plane's transponder and acts on those replies. Your TCAS reports to the other aircraft via your own transponder. There is no TCAS to TCAS direct link, as there is no ATC SSR uplink to your plane, save for the reply lamp of the Mode AC world. The TCAS processor is just an airborne ATC Secondary Surveillance Radar.
A good way to operationally test your TCAS on the ground is to block the radio altimeter RF signal so it thinks you are above 2500 feet. Your TCAS then thinks it is at altitude, and will give you TAs and RAs from real traffic in the area. It has no effect on airborne traffic, as your transponder is still reporting ON Ground, and within 180 feet of field elevation.
GB