The FMA changes to ARM at 800’ on NG series and 400’ on CL series. The logic allows the auto throttle to react to mode changes eg N1 or indeed to a second press of TOGA - below this height a second TOGA press will only move the thrust limit bugs to display the full thrust limit with no corresponding change in actual thrust, once FMA changes from THR HOLD to ARM a second press of TOGA will advance the thrust levers to full thrust.