Since version 2.1

Syntax:

memset <int source_address>, <int length>, <byte fill_value>

The MEMSET commands calls a built-in routine that sets length number of bytes in memory to fill_value starting from source_address. The same functionality can be achieved with FOR ... NEXT and POKE, but MEMSET is considerably faster.

Example:

rem -- clear the screen
memset 1024, 1000, 32

which is equivalent to:

for n = 1024 to 2023
  poke n, 32
next n