TOPS20monCallUG

This "TOPS-20 Monitor Calls User's Guide" (AA-D859C-TM), revised in September 1985, serves as an introductory manual for assembly language programmers unfamiliar with DECSYSTEM-20 monitor calls. It details how user programs can access various system services, including input/output, process control, file handling, and device control, under the TOPS-20 V6.1 operating system.

The manual is structured to progress from fundamental to more advanced concepts, covering key areas such as:

• Terminal Input/Output: Basic operations for reading and writing bytes, strings, and numbers to/from the user's terminal.
• File Management: Establishing Job File Numbers (JFNs), opening and closing files, and methods for transferring data (sequential, nonsequential, and page-mapped data).
• Software Interrupt System: Setting up, enabling, activating, and processing interrupts generated by the system, terminals, or other programs.
• Process Structure and Communication: Creating, managing, and interacting with multiple processes within a job, including direct control, shared memory, and using the Enqueue/Dequeue (ENQ/DEQ) and Inter-Process Communication Facility (IPCF) for resource allocation and message passing.
• Extended Addressing: Guidance for programmers on using 30-bit addresses and adapting programs for multisection memory environments.

This guide supersedes AA-D859B-TM and is designed to introduce the functionality, often referring users to the "TOPS-20 Monitor Calls Reference Manual" for more complete descriptions of all calls. Prior familiarity with MACRO language, DECSYSTEM-20 machine instructions, and the TOPS-20 Command Language is assumed.