TOPS-20 Monitor Calls Reference Manual

This document serves as a comprehensive reference for assembly language programmers using monitor calls (JSYS instructions) within the TOPS-20 operating system. It covers all monitor calls, including those for ARPANET and DECnet systems.

The manual is structured into three main parts:

1. Introduction: This section defines the conventions for using monitor calls and describes various argument types such as addresses, byte pointers, file handles, and process handles. It also introduces system date and time formats and general processing error handling.
2. Functional Organization of JSYS's: This part categorizes monitor calls by their function, providing an overview of calls related to:
   • Accounting: Managing job initiation, termination, and accounting information.
   • File Referencing: Handling file specifications, logical names, file handles (JFNs), and device access (treating devices as files).
   • Input/Output: Describing different data transfer methods, file byte counts, end-of-file limits, and I/O error processing.
   • System Information: Retrieving error mnemonics, message strings, and data from system tables.
   • Device Communication: Controlling various devices like card readers, magnetic tapes, line printers, and terminals.
   • Software Interrupt System: Managing interrupt channels, priority levels, and related processes.
   • Process Capabilities: Defining and controlling process capabilities and access control mechanisms.
   • Save Files: Explaining formats for nonsharable and sharable save files.
   • Input/Output Conversion: Converting between ASCII text and various numeric and date/time formats.
   • Archive/Virtual Disk System: Detailing terms and functions for archive and virtual disk operations.
   • Privileged Monitor Calls: Listing calls that require special system privileges.
3. TOPS-20 Monitor Calls: This section provides an alphabetical listing of each monitor call, detailing its purpose, numeric definition, accepted arguments, return values, and potential error mnemonics.

The document also includes appendices covering character collating sequences and system symbol definitions to aid programmers.