522 ISPS PRIMER FOR THE INSTRUCTION SET PROCESSOR NOTATION

The abstractions op, ib, pb, and pa allow the treatment of selected fields of the PDP-8 instructions as individual entities.

PARTITIONING THE DESCRIPTION
In ISPS, a description can be divided into sections of the form:

** section.name ** <declaration>, <declaration>,
. . .

** section.name ** <declaration>, <declaration>,
. . .

Each section begins with a header, an identifier enclosed between ** and **. A section consists of a list of declarations separated by commas. Section names are not reserved keywords in the language; they are used to convey to the users of the description some information about the entities declared inside the section. The register and memory declarations presented so far could be grouped into the following sections: