Supposedly also data for the proximity fuse should be sent to the missile.
Proximity fuse is a passive one, works differently than the active ones used by other SAM systems.
Hpasp Free SAM Simulator, "Realistic to the Switch" (U-2 over Sverdlovsk, B-52's over Hanoi, F-4 Phantoms over the Sinai, F-16's and the F-117A Stealth bomber over the Balkans.) http://sites.google.com/site/samsimulator1972/home