Fortran Subroutines for the Pdp-12

This document describes a package of eight subroutines and functions designed for real-time control of the PDP-12 computer. These programs allow a user to manipulate data acquisition and control functions—specifically the clock, display, A-to-D converter, sense switches, external line levels, relays, and left switches—directly from within a high-level FORTRAN program.

Key features include:

• Subroutines:

  • CLKSET: Initializes and controls the KW12-A clock.
  • CLKRUN: Monitors and senses clock interrupts.
  • RELAY: Controls the state of six relays.
  • DISP: Manages point displays on the VR-12 scope.

• Functions:

  • ISNS: Returns the status of sense switches.
  • IEXL: Returns the status of external lines.
  • IADC: Returns the decimal value of an A-to-D channel.
  • ILSW: Reads the octal equivalent of the left switches.

The document notes that while these subroutines provide ease of use, they do sacrifice some speed, resulting in a minimum sampling interval of approximately 4 ms. Included in the documentation is a demonstration program that generates a time interval histogram and provides the full assembly source code for all subroutines.