I've known about the popular HT12E & HT12D encoder-decoder pair of ICs for a long time but never had any reason to use them until now. I don't have them in stock and and can't try them out now. So I would like to request clarification about one aspect which is vital for my intended application.

The encoder datasheet says that the inputs are internally pulled high in the absence of an external input and sample circuits always show that those inputs should be pulled low for signalling.

On the other hand, the decoder datasheet says that the output "power-on state is low". I take this to mean that the outputs are low in the absence of any data input.

So, when the encoder and decoder have established contact, is the decoder output low when the encoder input is high? In other words, is there a polarity reversal between encoder input and decoder output?

OR, does the decoder output change state and go high as soon as communication is established (while the encoder input is still high)?

The datasheets are at
https://www.holtek.com/documents/101.../2_12ev120.pdf
https://www.holtek.com/documents/101.../2_12dv120.pdf

Below is a minimalistic circuit for illustration.
Click image for larger version. 

Name:	HT12E-HT12D.png 
Views:	7 
Size:	7.0 KB 
ID:	155247