The SNR is a utility module for multi-row sequencers such as our CGS359. While these sequencers have a fixed row output the SNR allows each row to be sequentially accessed at, typically, the 'start' of a sequence. So, with, as an example, the CGS359-8 which has 4 rows of 8 stepped outputs (4x8), adding the SNR will give the user a single 32-step (1x32) sequencer.
The [STEP] input is usually taken from the [PULSE] output of the 1st step of the sequence and so causes the SNR to select the 'next' row at the start of each sequence repeat. By gating this [STEP] input with an external signal, it is possible to add 'repeats' to each or any of the selected rows.
With the [STEP] input derived from the sequencer itself, the row selection is synchronised to the sequencer pattern itself. You could, of course, derive the [STEP] signal from any other suitable clock source in your system to generate non-synchronised selection of the rows.