
**Not mandatory.** Only needed if a VSCP boot-loader algorithm is used.

NACK the reception of data block. This event has no meaning for any node that is not in boot mode and should be disregarded.

 | Data byte | Description | 
 | :---------: | ----------- | 
 | 0 | User defined error code. | 
 | 1 | MSB of write pointer.    | 
 | 2 | write pointer.           | 
 | 3 | write pointer.           | 
 | 4 | LSB of write pointer.    | 

The write pointer is the actual pointer after the last data has been written i,e the next position on which data will be written. 
