M921

This document is a schematic for a Digital Equipment Corporation Device Code Select Jumper Board, identified by part number M921-0-1, copyrighted 1969.

Its primary purpose is for test and maintenance, detailing the proprietary circuit design.

The schematic includes:

• Pin Signal Assignments: Tables provide "OUT" signals (MB3 through MB8, associated with sets of pins like AI, BI, CI for Device A, B, and C) and "IN" signals (MB3(0) through MB8(1), associated with individual input pins like D2, E2).
• Circuit Diagram: A detailed drawing illustrating the connections between the input pins and various output pins/signals.
• Split Lugs: The diagram uses a specific symbol (a circle with a dot) to indicate "split lugs," which are configurable connection points, likely used for jumpering to select different device codes or configurations.

Essentially, the board provides a configurable interface for routing various input signals to specific output signal combinations to facilitate device code selection.