Texas Instruments VPU200

This device called "Video Programming Unit" or VPU is an industrial computer from 1980s used to program PLC control units with ladder logic programs. Then the program could be printed or stored in the controller's memory to be executed. It has also a key lock, which, by software, protects the memory from overwriting. The machine contains everything needed: Floppy disk drive, keyboard, display and power supply. Additionally, serial ports are available for expansion or connecting a printer to print the program out. Inside, it is powered by TI TMS9900 microprocessor known from TI99 microcomputer, but has 128kB of system RAM as well as 128kB of additional RAM. Originally the floppy drive used was a Kodak drive with very peculiar format allowing to put 2.7MB on a single 5.25" disk, but not all units had this drive.
Although it has been made in 1984, it has an older, but well tested technology inside. Most of logic is made in TTL chips and only the most complex things like clock generation, Serial I/O, disk control or ports expansion is made on VLSI chips and they are a bit aged even for 1980s. The display buffer is implemented on recirculating shift registers which is a very Apple I-like technology and these parts were obsolete even in 1980s. However, using these registers allowed to have a reliable picture board with almost no VLSI chips so it could be fixed using off-the-shelf components available in the storage of industrial electronics workshop. And that's how industrial computers have been built.

Manufacturer Texas Instruments

Origin USA
Year of unit 1984
Year of introduction ?1984?
End of production ??
CPU Texas Instruments TMS9900
Speed ?MHz
RAM 128kB (ROM OS)
128kB (System addiitonal RAM)
(simple diagnostics + loader)
Colors: 2
Sound: Beeper
OS: Monitor, ???
Display modes: Text: 80x25?  


Media: Built-in 5.25" FDD  

Power supply:


Built-in switching power supply

I/O: Built-in keyboard
2 RS232 ports for connecting printer and ?PC? (?modem?)
Expansion port? (5TI)
CRU port ???
Possible upgrades: ??
Software accessibility: Probably impossible  

I don't know much about my unit except that it was very dirty, stored in poor conditions. I probably opened it first after years, as I have not seen any traces of manipulation. Two boards are not present, but they are missing in other units too so they are some expansions.
A non-typical thing is a floppy drive used in my unit, it's Shugart SA455-2 (documentation) which is a normal 40-track drive, and usually these TIs had a specific Kodak drive which could squeeze even 160 tracks with 17 sectors per track. Although this format was extremely fragile, it was possible to fit around 2.7-3MB on a single 5.25-inch disk.

Contents: Starting Disassembly Links


WARNING: This computer has about seventy (70) 4116 DRAM chips. These chips fail when there is no -5V power. So if in doubt, DO NOT start up right off the bat, but test the power supply first!

To test the power unit: Disconnect power supply cable. Remember that some grounds are not connected in power supply but are connected in backplane. Now what you need to check is three 12V phases (mainboard, display and floppy phase, they are separated in the hardware and never connected to each other), +5V phase distrivuted on a few wires, -12V phase and the most important -5V phase. Be quick as the power supply should not operate for too long without load and coils make noises in such condition!
If all voltages are OK, try starting it up... with memory board removed. My unit boots its firmware without memory board as it uses 128k on floppy disc controller board for it. If in such case there is still -5V, turn the machine off and install board with 4116.
I cannot tell more about this unit as I don't have any disks and software for it.

For your convenience, here is the pinout of power supply unit in the PSU. The connector to backplane is 1:1.

| 1 2 3 4 5 6 7 8 9 1 1 1 1 1 |

1 - +12V for floppy drive
2 - Power-on
3 - -5V
4, 5, 8 - GND (Logic)
6 - GND for floppy
7 - GND for display
9, 10, 11 - +5V for logic and FDD
12 - +12V for logic
13 - +12V for display
14 - -12V for logic

(display connector is similar, 9-pin, counted the same way 1, 9 - GND; 6 - +12V; 5,7,8 - signals; all other are NC).

So after pressing the power switch, it should beep a few times and finally, after a short time, show a picture on screen. There will be a menu for booting from disk, formatting disk, copying disk or running diagnostics.


You need a long screwdriver which ends with a hexagonal socket. It must be long enough to reach between the display unit from the top, to remove screws from there. Another problem is that literally no metric hexagonal sockets fit these screws, so I needed to modify a 6mm socket using a flat file to enlarge the socket a bit.
The general order is:
0. Main casing: Screws at the rear-bottom, screws in front.
1. Remember to clean the air filter on the side of boards cage! It is usually dirty.
2. Remove two metal brackets locking boards, now boards can be removed They are color-coded.
3. Remove 4 screws using the hex-socket screwdriver to remove display unit.
4. Remove floppy drive (remove its side screws and shove to front).
5. Remove Floppy drive cage, also these hex screws on the bottom (power supply unit becomes visible).
Because the bottom may be shielded, retain the rubber grommets which should be under display unit.


http://web.archive.org/web/20010710055831/http://www.sea.siemens.com/automat/product/plc/505/au505dl.html - Some downloads for Simatic 505 and 560 PLC controllers.