Well, here it is for one aircraft type, straight from the Boeing 777 Manual to you -
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Rejected Takeoff
Selecting RTO (rejected takeoff) prior to takeoff arms the autobrake system. The RTO mode can be selected only on the ground. The RTO autobrake setting commands maximum braking pressure if:
(1) the airplane is on the ground
(2) groundspeed is above 85 knots, and
(3) both thrust levers are retarded to idle.
Maximum braking is obtained in this mode. If an RTO is initiated below 85 knots, the RTO autobrake function does not operate.
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That applies to the B777. Other aircraft may vary considerably.
Regards,
Old Smokey