Have you tested the HT-12E directly wired to the HT-12D (with a common ground), without
a microcontroller in the circuit, and still seen no response on the decoder outputs?

If the direct-connect test fails, then I would suspect one of the following;

1. You have a different address on the decoder than what's set on the encoder.
2. You have no common ground between the two ICs.
3. You have a bad encoder or decoder.

The encoder data out to decoder data in is the 1st test we recommend to anyone having
problems. This test helps determine if the problem is with the encoder/decoder ICs or the RF
stage.