TM5000 GPIB Control System

Professional Instrument Control for DOS Systems

Figure: Gridcase 1520 running a Tektronix TM5006A modular measurement system via GPIB control — FFT spectral analysis of a precision voltage reference standard.

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🎯 Overview

The TM5000 GPIB Control System is an instrument-control and data-acquisition platform for DOS systems. Originally developed for the Gridcase 1520 portable computer, it provides control of Tektronix TM5000-series instruments over a GPIB (IEEE-488) interface, using the Personal488 (IOtech/CEC) driver.

This repository preserves the entire history of the project — from the earliest binaries through the current modular source — which makes it a useful study in how a constrained 16-bit DOS application evolved. The current, buildable source is in src/; every prior version is kept under archive/.

📁 Repository layout

TM5000/
├── src/                 Current canonical source (v3.6) — build from here
├── archive/             Frozen historical versions (reference only)
│   ├── v1-binaries/     V1.8 / V1.9 executables (no source survives)
│   ├── v2-source/       V2.0–V2.9 monolithic single-file C
│   └── v3.0/ … v3.5/    Earlier modular releases (each self-contained)
├── docs/
│   ├── BUILD.md         Toolchain + build/run instructions
│   ├── ARCHITECTURE.md  Architecture notes (v3.6)
│   ├── FINDINGS.md      Cross-version regression analysis (what worked vs broke)
│   └── changelogs/      Per-version changelogs (v3.5, v3.6) + release notes
├── CHANGELOG.md         Consolidated version history
├── CONTRIBUTING.md
├── README.md
└── LICENSE

🔧 System Capabilities

Instrument Support

• DM5010 — 4½-digit multimeter with high-speed acquisition
• DM5120 — 6½-digit precision multimeter with advanced math functions
• PS5004 — single-channel precision power supply (0–20 V, 300 mA)
• PS5010 — dual-channel power supply with logic supply (0–32 V, 0.75 A)
• DC5009 — universal counter/timer with advanced triggering
• DC5010 — enhanced counter with rise/fall time measurement
• FG5010 — function generator

Data Acquisition

• Up to 10 instrument slots simultaneously (single GPIB bus)
• 1024 samples per module (v3.4+)
• Sample intervals from 100 ms to 10 s, plus custom rates
• Continuous real-time monitoring with live display
• Dynamic buffer management within the 640 KB DOS budget

Mathematical Analysis

• FFT (power-of-2, 64–1024 points) with Rectangular/Hamming/Hanning/Blackman windows
• Statistics: min, max, mean, standard deviation, RMS
• Waveform math: differentiation, integration, smoothing/filtering, scaling, offset, dual-trace operations, curve fitting, correlation, linear regression
• Automatic peak detection
• Optional 80287 coprocessor acceleration (pure-C FFT path)

Display & Visualization

• CGA graphics (320×200, 4-color) with engineering grid
• Up to 10 simultaneous color-coded traces
• Auto-scaling with manual override; zoom/pan; interactive cursor measurements
• Automatic V/mV/µV unit scaling

Data Management

• Native .tm5 measurement files and .cfg configuration files
• Export to CSV / text / PostScript (enhanced CSV with metadata in v3.5)
• Configuration profiles — save/restore complete system setups (v3.5)

Printing

• PostScript output and Brother dot-matrix support over LPT1
• Custom headers, automatic legends, IEEE scientific-notation formatting

🏗️ Architecture

The v3.x series is a modular rewrite of the original monolithic v2.9 (which had outgrown the DOS 64 KB segment limit). The current source is ~21,650 lines across the files below. Full detail: docs/ARCHITECTURE.md.

Area	Files
Core	main.c, tm5000.h (the single shared header)
GPIB / driver	gpib.c/.h, ieeeio_w.c, ieeeio.h (Personal488 glue)
Instruments	modules.c/.h, module_funcs.c/.h
Data & export	data.c/.h, export_enhanced.c, config_profiles.c/.h
Math	math_functions.c/.h, math_enhanced.c
UI / display / print	ui.c/.h, ui_math_menus.c, graphics.c/.h, print.c/.h
Assembly (286/287/CGA)	cga_asm.asm, mem286.asm, fixed286.asm, trig287_simple.asm

The four assembly modules are assembled and linked but not currently invoked from C (only extern declarations exist) — treat them as optimization scaffolding. See docs/ARCHITECTURE.md and docs/FINDINGS.md.

Version evolution

Version	Release	Key change
v3.0	June 2025	Modular architecture; DOS segment compliance
v3.1	June 2025	Full instrument support; 287 optimizations
v3.2	June 2025	Stability; FFT printing; configuration persistence
v3.3	June 2025	File-I/O reliability; symbol-conflict resolution
v3.4	July 2025	1024-sample buffers; ~22% memory reduction
v3.5	July 2025	Configuration profiles; enhanced export; enhanced math
v3.6	June 2026	Regression fixes (FFT, DM5120, stats, import) + new math (polynomial/exponential curve fit, cross-correlation, phase/delay) + linker dead-strip for a smaller binary

🔨 Requirements

To run: IBM PC-compatible 80286+ · 640 KB RAM (1 MB recommended) · CGA graphics · MS-DOS 3.3+ · a Personal488 (IOtech/CEC) GPIB interface with its DOS driver (DRVR488.EXE). An 80287 coprocessor and a Microsoft-compatible mouse are recommended. The original target was the Gridcase 1520 portable.

To build: OpenWatcom C/C++ 1.9 (16-bit DOS target) plus its assembler. See docs/BUILD.md.

💾 Quick start

# Build (from the source tree)
cd src
wmake                     # produces tm5000.exe (~270 KB, dead-stripped)

# Run on DOS / DOSBox
#   1. load the Personal488 driver (DRVR488.EXE) if using GPIB hardware
#   2. TM5000.EXE

Basic flow inside the program:

Main Menu → Configure Modules → [select instrument] → [set parameters]
          → Measurement → [continuous / single] → [start acquisition]
          → File / Export → [save .tm5 / .cfg / CSV / PostScript]

✅ Fixed in v3.6

Every limitation catalogued for v3.5 has been traced to a specific cause (in several cases to a prior version where the behavior worked) and fixed in v3.6. Details: docs/changelogs/CHANGELOG_v3.6.md; full code-referenced analysis: docs/FINDINGS.md.

• Computed FFT/math result traces are no longer wiped on entering continuous monitoring.
• FFT low-frequency dB content is no longer clipped (the documented-but-missing fix is now applied).
• The FFT spectrum is no longer silently truncated at small output sizes (peak-preserving decimation).
• DM5120 buffer fills no longer stall waiting on an external trigger (defaults to internal; EXT opt-in).
• Enhanced Statistics labels dB/Hz/Ω/A traces correctly instead of as volts.
• .tm5 import resynchronises to the data marker, tolerating a sample-count mismatch.

Also new in v3.6: polynomial & exponential curve fitting, cross-correlation, and phase/delay analysis (previously stubbed) are now implemented. The build enables OpenWatcom dead-code elimination (-zm + OPTION ELIMINATE), so tm5000.exe is ~270 KB — smaller than v3.5 despite the added features. See CHANGELOG.md.

Remaining lower-priority items (header/API-hygiene cleanups noted in the review pass) are tracked for a future release.

🔬 Educational use

The TM5000 system is a useful platform for studying DOS/16-bit software architecture, GPIB/IEEE-488 instrument control, real-time systems under tight timing, and programming within hard memory constraints.

📄 License

Provided for research and educational purposes. See LICENSE.

Copyright © 2025 — For Educational and Research Use