96 Impala SS passkey (no start)

Hello. Have a '96 Impala SS. Car was fine, with a strong battery. Battery was disconnected recently. When reconnected, car will not crank. Intrument panel
goes through the self test when ignition is turned on, but will not crank. Does the passkey need to be re-learned / re-programmed by the computer? If so, does anyone know how to do this? For example, a 1997 Silverado has to be put in neutral and the brake pedal pressed 3 times (intuitive). Again, the battery is strong, the cables are tight, and the key w orked (started the car) before the battery was disconnected, so I doubt that it is a dirty key.
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