Tektronix 4051 Hardware Emulator

[nikola-wan]

I have been looking at the SWTPC 6800 programs (Southwest Technical Products Computer). This personal computer was made in the late 1970's, with similar chassis construction to the Altair 8080 computer, but different bus interface for the cards.



There was a lot of third party hardware and software developed for this computer including floppy and hard disk controllers and the FLEX operating system. Since the 6800 CPU was limited to 64KB of address space, and the SWTPC only contained a boot ROM, there were Assemblers, Editors, several different BASIC interpreters, sdBASIC compiler, several c-Compilers, PASCAL, Forth, PLM and other languages available.

They had a strong user group with lots of activity and a magazine, and there is a full SWTPC emulator with many 6800 disks available at:

http://www.evenson-consulting.com/swtpc/default.htm

I have been interested in getting some of the SWTPC programs ported to the Tektronix 4050 series (yes - entire series as the 4052/4054 included compatibility with the entire 6800 instruction set with the exception of the DAA instruction).

I also found another person that has been porting SWTPC programs to his custom 6800 board:

http://www.waveguide.se/?article=calixto-island-adventure



Daniel has written several programs to help with converting the SWTPC programs to his hardware, and has also designed his own floppy disk OS using an SD card for storage!

I believe someone could build a hardware emulator of the 4051 with a 6800 CPU board like Daniels, add the 4051 ROMs, and add 4051 graphics emulated with a small micro running the Tektronix 405x graphics emulator commands to a display!

Since almost all the Tektronix 4051 programs run from tape, which is emulated in the 405x emulator, I can easily imagine that David's SD card hardware design could be modified to provide the program storage! David added a "CD" command to allow multiple directory support from the SD card, which could easily be added to this 4051 hardware emulator to run ALL the 4050 programs that have been posted to github and additional SWTPC programs ported to this hardware.

Are any of you hardware and software developers - interested in this project?

 

[jdreesen]

I sold my SWTPC system a year or so ago...Mine had a built-in 24x80 terminal on a SS50 board and was upgraded to 6809.

You could easily start from my bit-bucket setup I created in 2019 : 2 stackable PCB, one with keyboard and 12 digit 7-segment display, the other the CPU-board.
The CPU-board can be stuffed with 6800 or 6802, has 64 K of SRAM and 32 K of Eprom. Also one 6850 serial channel. The memory map is flexible and can be rearranged by reprogramming the GAL.
It currently runs the Tektronix Boardbucket BASIC. I also intended to make it SWTPC combatible, but never finished the 3e PCB with the floppycontroller. I was sidetracked by the 4052 extended RAM board....
Also I never made the software adaption required to run the Motorola SBUG monitor on the display board.



I still have a number of empty PCB's left if anyone wants to continue the project !( I will, but not in the near future...)

Jos

 

[nikola-wan]

Jos,

Cool CPU-board, Jos!

The 1975 Tektronix 4051 was far ahead of its microcomputer competitors - but as it targeted commercial users as a vector graphics workstation computer, it was an unsung complete system in all the microcomputer timelines that only considered consumer computers with no graphics or low-resolution bit-mapped graphics.

Certainly your CPU-board targeted the Tektronix prototype board for the 4051, but did not have the complete BASIC with graphics of the 4051 and therefore unable to run any of the 4051 programs other than plain text BASIC programs on a separate serial terminal.

The attraction of the late 1970's consumer microcomputers was the very low cost (hundreds not thousands of dollars), but they also had no user software except for BASIC. Contrast this with the Tektronix 4051 which included a complete computer system with 1024x780 vector graphics, 32KB BASIC in ROM including support for GPIB peripherals, keyboard, DC300 data tape drive, and peripherals like floppy drive, printers, plotters, joysticks and graphics tablets. In addition, Tektronix launched the 4051 with software libraries like Electrical Engineering, Drawing, Statistics, and Program Management. Biggest obstacle to success was high system price - but it was attractively priced against mini-computers, and targeted individual users as graphics workstations.

The Motorola 6800 8-bit CPU was very limiting (performance, memory capacity, instruction set), and as the 6800-based microcomputers moved to the newer 6809 CPU, Tektronix replaced the 6800 with a custom bit-slice 16-bit CPU to provide about 10x performance improvement and double the memory capacity to 64KB. However, Tektronix stuck with BASIC in ROM, instead of offering the ability to use other programming languages as the microcomputer market exploded in the 1980's.

My retro-interest in adding SWTPC programs to the Tektronix 4051 may be a bit over the top at this point. I think I have collected and posted most of the programs that would be of personal interest (games) and many that were of commercial interest. I learned a lot using a 4051 at work in the late 1970's - and it was my first experience with a personal computer, although I had built a COSMAC Elf from the Popular Electronics articles - I didn't find it very compelling.

My experience with the Tektronix 4051 helped me with my later professional career, working at Texas Instruments as the architect for the portable Pro-Lite CMOS 8088 computer with a B&W graphics LCD screen in the early 1980's, followed by working at Compaq Computer on the Deskpro 286, quickly followed by the Deskpro 386 and 486. Until the late 1980's with the introduction of the VGA, the graphics capability of these PCs was nowhere near the capability of the 1970's Tektronix 4050 computers.

I'm fortunate to have working Tektronix 4052 and 4054A computers, so I don't need a hardware emulator.

I enjoy using Jos' Tektronix 4052/4054 Multi-function ROM Pack - which not only supports all the ROM Packs but adds a Real-Time Clock and additional serial port, and Jos' latest Auxiliary Memory ROM Pack which adds 512KB of NVRAM file storage and eliminates the need for a working DC300 tape cartridge AND eliminates the need for the huge 4907 Floppy Drive system for fast program loading.

Jos, thank you for your efforts in supporting the Tektronix 4050 computers!!

Plus my thanks to daver2 and Philcogrump for creating a very good 405x emulator for those that would like to experience what the 4051 vector graphics computer could do.

 

[Vermithrax]

Jos:

I found this article after digging into the work that Daver2, Monty and Falter did on the Tektronix 6800 Board Bucket. I have a partial disassembly started, and from the discussion I can see where the COM Port ACIAs are initialized and some hints as to where the PIAs and displays are written to.

As I still have my SWTPc 6800, I am curious about porting DDT and Tektronix BASIC to that machine (sorry, no floppies), did you resolve the hardware addresses in the $DA1B to $DA88 and other ranges to hardware?

Regards,


Nelson

 

[jdreesen]

The main PCB just has a GAL that does the decoding. By changing the GAL contents you can pretty much redesign the whole memory map as to your whishes.
Schematic is attached below. The main board just has a serial interface, that's all. So no, hardware is not ported, although the PCB should support it.

View attachment BB.pdf

 

[daver2]

Jos:

I found this article after digging into the work that Daver2, Monty and Falter did on the Tektronix 6800 Board Bucket. I have a partial disassembly started, and from the discussion I can see where the COM Port ACIAs are initialized and some hints as to where the PIAs and displays are written to.

As I still have my SWTPc 6800, I am curious about porting DDT and Tektronix BASIC to that machine (sorry, no floppies), did you resolve the hardware addresses in the $DA1B to $DA88 and other ranges to hardware?

Regards,


Nelson

Welcome to the thread, and welcome to VCFED.

I will have to go back and check my notes for that...

It does sound an interesting project to get them running on a different hardware platform though. It should be simpler for DDT (being serial already). The TEK BASIC itself would be a good choice (as it is an excellent BASIC in my opinion) but would be problematic because of the display. I do, however, have some VHDL code somewhere for an FPGA to emulate the vector display of the Vectrex computer - and I was (at some point) considering modifying it for use as a 4051 look-alike display. The same project has come back again in the guise of a storage monitor display device for my DEC PDP-8/E VC8 display...

Dave

 

[Vermithrax]

Jos - thanks so much for the schematic to the CPU board! Very nice design.

Regards,

Nelson

 

[daver2]

I have resurrected the Tektronix 6800 Board Bucket thread and added some more information to it. Hopefully, this should keep everything together.

Dave