MAINDEC-4 MulDiv

MAINDEC 4 is a maintenance program developed by Digital Equipment Corporation in 1963 to test the multiply and divide capabilities of DEC computer hardware.

Key features and functions:

• Purpose: It verifies the functionality of both automatic multiply/divide operations and the Multiply Step (MUS) and Divide Step (DIS) instructions.
• Methodology: The program generates random numbers, performs multiplication and division, and then compares the results produced by the hardware with those calculated by a software simulator.
• Operation: It runs continuously, using the typewriter to output detailed error messages whenever a discrepancy is detected between the hardware and simulator results. A second pass is made on errors to provide more granular simulator output.
• User Control: SENSE switches allow the user to inhibit specific tests (e.g., only test multiply, or only test divide), suppress error printouts, or control the random number generator's advancement. The starting address (0000 for automatic MUL/DIV, 0001 for MUS/DIS) determines which set of instructions is tested.
• Error Reporting: Error messages provide comprehensive information, including the contents of key registers (AC, I/O, MB) before and after the instruction, the expected result, and the actual result obtained from the hardware.
• Troubleshooting: The document also provides guidance for advanced troubleshooting, including suggestions for using marginal checking and methods to single-step through the multiply and divide timing chains for in-depth diagnosis.