What is a USERCODE instruction?

The USERCODE is an optional instruction in the boundary scan description language (BSDL) that allows a 32-bit user programmable identification code to be loaded and shifted out for examination. The purpose of the USERCODE is to expand the IDCODE in situations where programmable devices such as programmable logic device (PLD) can be used to identify the version of the programming code.

Example:

Attribute USERCODE_REGISTER of My_IC : entity is
-- 3A1B00F3 hex programming ID
“0011” & “1010” & “0001” & “1011” &
“0000” & “0000” & “1111” & “0011”;