The thresholds at which the internal digital is able to properly detect a high vs. low transition are shown in the figure below. The key threshold voltage is 1.75 V for a high to be detected and -1.75 V for a low. However, at range between +/-1.13 V to +/-1.75 V there is a possibility that the digital will interpret this as a high/low signal but it is not certain until the 1.75 V threshold is reached.

For tones, the digital is purely looking at edge detection transition, so as long as there is a +1.75 V threshold polarity change to -1.75 V then the couplet will be detected properly. Therefore, the blank time where the signal may rise above 1.13 V after the tone couplet will be ignored.

For data communications, the threshold must remain above 1.75 V during the full 250 ns high and 250 ns low side to properly interpret the command.

Figure 3-1 Daisy-chain Receiver Threshold