**Mandatory.** Should be implemented by all level I devices.

Decrement a register content by one with no risk of it changing in between 

 | Data byte | Description | 
 | :---------: | ----------- | 
 | 0 | Node-ID                | 
 | 1 | Register to decrement. | 

Node should answer with [CLASS1.PROTOCOL, Type=10 (Read/Write register response)](./class1.protocol.md#type10).
