Inside SCRX2BC the signal is amplified and filtered in two stages between pins 14, 15, 16, 1, and 3. Pin 3 (DI) is the output pulse sequence that was picked up by the receiver; this is used as the input to the decoder. The SCRX2BC scans for the 4 long (synchronization) pulses and then counts the number of short pulses after them to determine which command was sent by the transmitter. The gain of the SCRX2BC stages is high enough to produce a pulse sequence at pin 3 even if no signal from a transmitter is present (it amplifies random noise), but the resulting sequence.
