CPDS Record Spooling and Page Counting

The Print Support Facility (PSF/VSE) program, for example, supports Advanced Function Printing (AFP) on laser printers and makes use of special Composed Page Data Stream (CPDS) records (also called AFP records) to carry information on setup and layout of pages to be printed. CPDS records are identified by a X'5A' Channel Command Word (CCW) operation code, and their data part is called a Structured Field. According to PSF Data Stream Reference (SH35-0073), the 3 byte coded Structured Field Identifiers, for example BEGIN PAGE (BPG), are used to interpret the information of CPDS records correctly for printing of image data.