The Tektronix 468 is a wonderful instrument, being both a solid analog scope with a real electrostatic CRT and being one of the first digital scopes, designed around an Intel 8085 CPU.
The Tektronix 468 is actually a hybrid scope, being an analog Tektronix 465B oscilloscope with an integrated digital section. The scope can run in both analog and digital mode. There is plenty of information available about the Tektronix 465B but not so much about the digital section of the Tektronix 468. Dutchtronix has been researching the digital electronics of the 468, including analyzing and improving the Intel 8085 code that operates the digital section of the 468.
By today's standards the digital specs are not impressive and for real work, any cheap digital LCD scope is a better choice.
However, there is something magical about these 40 year old instruments that are still in perfectly good working order. Besides that, they display Scope Clocks much better than modern scopes! It something goes wrong, these scopes can be repaired. In those days, Tektronix did an excellent job documenting their products.
Well, partly. When the digital revolution started in the late 70s, the company was not setup for digital work. As a result, the internals of the software running the digital section of the 468 is not documented at all, besides publishing the memory mapped I/O addresses. The original firmware for the 468 was written in a language called Tesla, which stands for TEktronix System LAnguage. Unfortunately, the Tesla source code for the 468 has been lost because Tektronix didn't know how to archive it! This information comes from an engineer who worked on designing and building the 468. The last software version published by Tektronix for the 468 is V2. Dutchtronix had to decode and analyze the binary code as present in the two ROMs (U565 and U575) to reproduce the firmware code.
The resulting 8085 Assembly Language source file is on Github. The assembled version of this code is bit for bit identical to the combined ROM binaries of U565 and U575. Comments are limited but many meaningful labels were added.
This website is dedicated to researching and explaining the digital hardware and firmware of the Tektronix 468 as well as making improvements.
Tektronix 468 One Rom Solution
The digital section of the 468 has another problem: Rom Rot. The binary code was burned into Mostek Roms but these Roms became FRoms over time ("Forgetting Roms"): the bits inside the Rom could become corrupted causing the 468 to be unusable. To make matters worse, the 24-pin 8K byte Roms used could not easily be replaced with Eproms because newer 27(C)64 Eproms use 28 pins. The 468 uses 2 of these 8K Roms for a total of 16K bytes of code.
Many home grown solutions have been published making adapter sockets using wire connections, removing pins, shielding pins etc. Vintage Tek published an elegant replacement board but the Flash Chip used is currently in short supply.
Dutchtronix came up with a unique solution: rewrite the 8085 software so that it fits into one 8K byte Eprom and use a 2764 adapter board to provide a plug and play solution.
Interested in adding firmware: Dutchtronix 32KB Unlocker (details to be added)
