Start of logical block. All labels, defined in this block, are local. It means you can’t reference them from outside the block. If you want to define a label globally, simply prefix it with ‘@’, like @LABEL: Good idea is to enclose INCLUDEd code into block. Block can have its own name, e.g. .block serial It is usable with .include directive to include only specific block from a file. Just use .include library.a80:serial - syntax is file:block - with a colon as a separator.