M253

This document is a schematic diagram for a 12-bit, 16-word memory module, identified as M253-0-1, designed by Digital Equipment Corporation in 1971 (Revision B).

The circuit's core functionality relies on:

• Three DEC7489 Integrated Circuits (E1, E2, E3), which are 16-word by 4-bit RAMs, collectively forming the 12-bit wide memory.
• DEC1074H00 (7400 series NAND gates, E4) for implementing control logic, including "CHIP SELECT".

The memory module features:

• Address Inputs: Four address lines (K1, S1, A1, N1) to select one of the 16 words.
• Data Inputs: Twelve data lines (D0-D11) for writing data into memory.
• Data Outputs: Twelve data lines (O0-O11) for reading data from memory.
• Control Signals: "WRITE ENABLE" and "CHIP SELECT I".

Support circuitry includes various capacitors (e.g., 0.01uF for decoupling, a 68uF electrolytic for bulk filtering) and resistors (e.g., 330 ohm, 750 ohm) for power filtering and biasing. Power is supplied at +5V, with specific pin assignments for power and ground noted for the ICs.

A comprehensive parts list details all components used, including the specific ICs, resistors, capacitors, and mechanical items like a "FLIP CHIP" handle and eyelets, indicating the module is designed for an etched circuit board. The drawing was made by Nancy Hoore.