This is the story about the Tektronix 7854 oscilloscope, built in 1980. This was the first 16-bit microprocessor-controlled digital storage oscilloscope built by Tektronix, in Beaverton Oregon. This was the first microprocessor-based digital oscilloscope to hit the marketplace by any manufacturer. It used a Texas Instruments TI-9900 microprocessor because it was the first 16-bit CPU. Intel only had the 8-bit 8080 microprocessor at this time and the 8086 was released after developing the 7854 oscilloscope.

I became involved in the project after transferring from a computer systems group in Tektronix to become a firmware engineer on the portable field test unit that Bill Cox and I would develop and implement. I had been working at home on an experimental single-board computer based on the 9900 microprocessor and had gained experience programming it in machine language. My programming of the MicroLab Test System was done in Assembly language using a cross-compiler. A few algorithms were done in machine language because of the speed requirements needed. This photo shows the complete 7854 with the available plugin modules and the cart.

I designed and implemented the bootstrap loader, the kernel, and the operating system. I also developed the diagnostics software for self-testing the MicroLab system and some field test diagnostics for the 7854 oscilloscopes. The 7854 also had some self-test firmware built into itself. The hardware engineering team designed those tests. The 7854 also had a keyboard accessory for data input and control of the scope.

This is the 7854 and the MicroLab Test System. The 7854 oscilloscope is on the right. I worked on the MicroLab Test System, which is shown on the left.

I designed and implemented the bootstrap loader, the kernel, the operating system, and the system diagnostic tests. My friend was an electrical engineer who designed the main computer logic board and the memory boards.

The field test system would tell the field technician which boards in the oscilloscope were bad and then they could replace the board and fix the scope without sending it back to our factory for repair. The MicroLab used signature analysis to design a troubleshooting tree. The instrument used to generate the signature tree was the HP 5004A Signature Analyzer.

These two photos show the MicroLab field test unit. The top picture shows the two ribbon cables which connect the MicroLab test computer to the 7854 Oscilloscope.

This photo shows the cables extending to the top of the 7854, connecting to the bus with a special adapter.

The 7854 Oscilloscope and the MicroLab Test System were state-of-the-art in design and technology in 1980. Having said this, there were limitations in things that could be done due to limited technology at that time. These limitations were addressed with some clever design by the 7854 hardware engineers.

7854 Digital Oscilloscope History
The 7854 digital oscilloscope, manufactured by Tektronix, was introduced in 1980 and quickly became a game-changer in electronic instrumentation. With its advanced features and user-friendly interface, the 7854 set new standards for oscilloscope performance and became the industry standard for decades.

Before the introduction of digital oscilloscopes, like the 7854, most oscilloscopes were analog devices that relied on cathode ray tubes (CRTs) to display waveforms. While analog oscilloscopes were useful, they had several limitations. For example, they had limited bandwidth, which meant that they could only display signals up to a certain frequency range. Additionally, analog oscilloscopes were susceptible to drift, meaning that their readings could change over time.

The 7854 digital oscilloscope was revolutionary because it used digital signal processing to convert analog signals into digital signals that could be analyzed and displayed on a screen. This allowed the oscilloscope to have much higher bandwidth and accuracy than analog oscilloscopes, it also helped with issues like drift. The 7854 was also one of the first digital
oscilloscopes to incorporate a microprocessor, which allowed it to offer advanced features like digital storage, automatic measurements, and waveform averaging.

One of the key features of the 7854 was its ability to store waveforms digitally. Before digital oscilloscopes, engineers had to rely on analog methods like film cameras to capture waveforms for analysis. With the 7854, waveforms could be stored digitally and recalled at any time, allowing for much more detailed analysis of electronic signals. Another major advantage of the 7854 was its ability to make automatic measurements. Before digital oscilloscopes, engineers had to measure waveforms using rulers and other tools. With the 7854, the oscilloscope could automatically measure parameters like peak-to-peak voltage, frequency, and rise time, which made it much easier and faster to analyze electronic signals.

The 7854 also had a user-friendly interface that made it easy to operate. It featured a large, high-resolution screen that displayed waveforms in real-time, and it had a variety of buttons and knobs that made it easy to adjust settings and make measurements. Additionally, the oscilloscope had a built-in printer that allowed engineers to print out waveforms and measurements for documentation purposes.

The 7854 remained the industry standard for digital oscilloscopes for many years, and it was widely used in many industries, including electronics, telecommunications, and aerospace. The 7854 was eventually replaced by newer, more advanced digital oscilloscopes. Its impact on the field of electronic instrumentation cannot be overstated. The 7854 paved the way for digital oscilloscopes that are used today, and it remains an important part of the history of electronic instrumentation.

Purpose of the MicroLab Test System
The 7854 Oscilloscope was a very complex instrument. Even though it had its own self-test diagnostics built into it, some problems would exist causing it not to power up. This is where the MicroLab portable field test unit came into play. It was designed to troubleshoot the major problems in the field and be a tool to diagnose and fix the problems at the board level. Thus, the technician could swap out the bad board and not have to ship the scope back to the factory for
repair.

Testing the 7854 Oscilloscope in the Field
The MicroLab field test system is connected to the bus of the 7854 scope by flexible ribbon cables and a special adaptor, carrying signals from the MicroLab to the 7854 Scope. The MicroLab had its diagnostic test firmware but it contained special firmware designed to troubleshoot problems of the 7854 to its board level. By diagnosing the failures at the board level, the field service technician could replace the broken board with a new spare board, saving it from being shipped back to the Beaverton factory. The advantage of the field test unit was quicker turnaround on repairing the instrument and saving the cost of shipping for repairs.

Memory System Overview
Several technical challenges had to be overcome in the design of the MicroLab field test unit. Because of memory chip size limitations in 1980, all the required code could not fit in a single
memory board. The addressing capability of the 9900 microprocessor was one of the technical challenges that had to be overcome. It could only address one memory board at a time. The TI-9900 microprocessor only had a 16-bit data bus. This meant it could only address 64k bytes.

The OS, bootloader, and kernel were designed to run in 4 ROM memory banks. Once it was designed and tested, this code did not change.

The diagnostic test code resided in 4 EPROM memory banks.

The ROM space was located in the front, fixed memory space of the memory board. The diagnostic firmware resided in 4 different memory banks behind the ROM memory. Since the
4 total memory board, consisting of 256k total memory, could not be addressed at once. The hardware engineers designed a proprietary "bank-switching" technique which expands the memory available by fourfold. You could address any bank desired, but you “switched” to that bank before doing a diagnostic test.

The OS had to switch banks, depending upon the test being run.

Test Diagnostics
The PROM chips in each of the 4 memory banks contained a special function control table at the front of the memory address space. This function table was a matrix of pointers to functions that were the diagnostic test required. There was also a “bank switch” table which contained information for each diagnostic test, such as bank #, test #, and location of the function table.

Hardware
The hardware engineers designed a proprietary "bank-switching" technique which expands the memory available to the MicroLab by fourfold. You could address any bank desired, but you “switched” to that bank before doing a diagnostic test. The hardware switching and the firmware had to work closely to take advantage of this extended memory technique.

Development System
The code for the MicroLab system was written on a TI-9900 development system using 9900 Assembly language. A few functions had to be hand-coded in machine language for
maximum execution speed. After the assembly code was finished, a cross-compiler was used to convert the code to TI-9900 resident object code. This was a tedious process because assembly language required the use of registers to do all of your coding.