M7236

This document is an Engineering Change Order Log from Digital Equipment Corporation, detailing modifications for the M7236 KT11-D Memory Management unit, primarily used with the PDP-11/40 (and later PDP-11/35) processors.

The log covers a series of engineering changes and corrections, identified by "M7236-XXXXX" codes, implemented between November 1972 and October 1973. Each entry specifies:

• A problem description (ranging from signal loading, etch errors, clocking issues, and incorrect ROM words to complex memory management trap logic and bus error handling).
• The correction required, which often involves specific hardware modifications (e.g., component replacement, cutting etches, adding wires), ROM updates, or documentation revisions.
• The new M7236 DD revision created (sequential from "A" to "D").
• Effectivity details, including immediate in-plant rework and extensive field rework for all affected M7236 units, often specifying for all PDP-11/35 and PDP-11/40 systems with memory management.
• Estimated installation and test time for field reworks.

Key issues addressed include initial design flaws (loading, etching, clocking), critical ROM and trap logic errors affecting system stability and security (e.g., incorrect Program Status Word handling, false memory management traps), and corrections to rework procedures and parts lists. These entries demonstrate an iterative process of identifying, diagnosing, and rectifying technical issues in the memory management hardware and associated documentation during its early production and deployment.