Hi Leo,
A binary block is a standard data type specified in section 8.7.9 of IEEE 488.2 (called a "definite length arbitrary block response data" there).
Here's a quick summary of how they work:
#nddddxxxxxxxxxxxxxx.............
Where # signifies the start of an arbitrary block, n is the number of digits in the length (in ASCII), d are the digits of the length (also in ASCII), xxxxx is your binary data (the format of which depends on your configuration).
Here's an example:
#215THIS IS A BLOCK
For more information please refer to the standard and the following examples: https://forum.tek.com/viewtopic.php?f=580&t=133570