Teardown Datum 9390 GPS Time Code and Frequency Generator
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Firmware Archive
Datum 9390 GPS EPROM ARCHIVE
27C2048 PLCC (256KB) is the firmware for the GPS receiver engine itself. Two things confirm this:
Its byte pairs swapped from true memory order (a common artifact of dumping a 16‑bit‑wide part with certain EPROM programmers). Un-swapping it exposes a clean copyright string: Copyright (C) 1992,1993 Trimble Navigation Written by Paul Braisted, plus a long run of GPS-engine debug strings (Signal Processor error:, Blind search, Tracking set update, SVs visible, Different week, etc).
Datum 9390 DDISPLAY EPROM ARCHIVE
M27C1001 DIP (128KB) is the front-panel keypad/LCD controller separate MCU, plain 8-bit ASCII, no swap needed. It’s full of UI prompt strings (ENTER LATITUDE:, ENTER TIME, DOING GPS CORRECTION, GPS TIME NOT ACQUIRED, etc.)
X-Ray of M48Z350Y
Last Updated on August 31, 2026 by Steven Rhine