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Key generator - wanted item

PU-104 was a key generator for perforated paper tape, made around 1986 by Rohde & Schwarz (R&S) in München (Munich, Germany). The device was able to create long sequences of truly random numbers and send them to external paper tape puncher via its built-in V.24 interface.

The device is housed in a grey-and-blue Rohde & Schwarz enclosure that is typical for the era. It measures 34 x 21 x 14 cm and weights 6.3 kg.

At the front is a DB25/F socket (V.24/RS232) for connection of an external tape puncher. A rotary selector allows the number of copies (tapes) to be set between 1 and 9. Furthermore there are two buttons, marked NEW KEY and KEY OUTPUT, each with a corresponding red LED. The current status of the device is reported via a single digit 7-segment LED display. When in use, the display counts down the number of copies to be created.
PU-104 key generator

The device has built-in test equipment (BITE), which means that its functions are tested on start­up, but also continuously during its operation. Any errors are reported on the display. At the rear is a EURO-socket for connection to the AC mains, plus a 3-pin XLR/M socket for connection of two external batteries. On some versions of the PU-104, these batteries were placed internally.

It is currently unknown in what year the PU-104 was developed and when it was released, if it was released at all. Most of the components inside the device have manufacturing codes of 1983 and 1984, which suggests that development took place around that time. Two of the RAM chips have a date code of 1985 and one EPROM was issued on 28 October 1986, which indicates that it was probably released in 1986. If you have any further information about this device, let us know.

PU-104 key generator Front panel Rear panel
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PU-104 key generator
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Front panel
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Rear panel

Block diagram
Although we do not have access to the original documentation or circuit diagrams of the PU-104, we can make a few educated guesses about its operation, simply by studying the interior. Below is a block diagram that explains the global operation of the device. At the bottom left is a true random number generator, in which a diode is used as the source of evenly spread 'white' noise.

At the bottom right is the V.24 (RS232) output to the tape puncher. All parts are under control of a central processing unit (CPU) that has its own RAM and EPROM memory. It controls all functions of the device and validates the generated random numbers, raising an alarm when it fails.

The PU-104 consists of a strong metal frame with a heavy adjustable grip, and two blue case shells – one at the top and one at the bottom – hiding the interior. The interior can be accessed by loosening 4 bolts at either side of the device, after which the blue case shells can be removed.

Front and back panel are affixed to the extruded aluminium frame. The image on the right shows the interior of the PU-104/C1 after removing the two case shells and dismounting the front panel.

At the rear is a large mains filter that separates the PSU from the mains. The actual PSU consists of two large pre-fabricated MELCHER modules – a switched mode power supply (SMPS) and a DC-DC converter – that are located at the bottom. About 1/3rd from the rear is a vertical backplane into which three large PCBs are slotted. The front panel is connected to it via two ribbon cables.
PU-104 interior

The upper board contains the central processing unit (CPU), which is build around an Intel 80186 16-bit microprocessor with two MB8464 64kbit Static RAM 1 chips and two EPROMs. 2 A 3.7V SL-350 Lithium battery is present on the same board, to retain the contents of the Static RAM chips.

At the front edge of the processor board is a vertical PCB with 16 yellow LEDs that probably show the status of the processor's data lines. These LEDs are normally not visible to the user.

The middle board contains the V.24 or RS232 interface, which is built around an OKI M82C51 Universal Synchronous Asynchronous Receiver Transmitter (USART). At the front edge of this PCD are 7 green LEDs that show the status of the RS232 lines. These LEDs are invisible to the user. The row of big diodes that is present on this board, was probably for protection of the lines.

V.24/RS232 interfaces were fairly common in the 1980s and 90s for the connection of peripheral equipment like printers and modems. On PCs they are commonly known as COM-ports. The bottom of the V.24 board is heavily patched, indicating that this might be an early a prototype.

The bottom board is likely the most interesting one, as it contains a Random Number Generator (RNG). It is built around a noise diode with two PM156 Operational Amplifiers (OpAmps), that drive a JK flip-flop and several ripple counters. Also on this board is a 1 MHz/4MHz oscillator.

The board contains additional logic for checking the randomness of the generated noise. This is done by counting the occurency of each word-value and comparing it with a preset tolerance window, generating an SOURCE DEF alarm on the front panel display if it has become biassed.
Random Number Generator

The RNG occupies about half the space on this board. The other half is reserved for two batteries and three large capacitors (super-caps) that have not been assembled on the board shown here. Judging from the large number of patches and modifications and the absence of a serial number plate, the PU-104 shown here is probably an early development prototype or engineering sample.

  1. RAM = Random Access Memory.
  2. EPROM = Erasable Programmable Read Only Memory.

Case shell removed Upper board seated in the backplane PU-104 interior Three PCBs slotted into the backplane Mains filter located at the rear Bottom view Backplane Front panel (rear view)
Upper board Upper board - bottom view Middle board Middle board - bottom side Bottom board Bottom board - bottom side Unknown processor on the upper board Random Number Generator (RNG)
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Case shell removed
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Upper board seated in the backplane
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PU-104 interior
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Three PCBs slotted into the backplane
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Mains filter located at the rear
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Bottom view
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Front panel (rear view)
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Upper board
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Upper board - bottom view
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Middle board
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Middle board - bottom side
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Bottom board
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Bottom board - bottom side
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Unknown processor on the upper board
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Random Number Generator (RNG)

Help required
At present, we have no further information about the PU-104, except for the Operating and Service Manual of the V.24 card (PU 104 S2), which is available for download below. If you know what the device was used for and by which organisation(s), or if you have any further information or documentation – like a user manual, a service manual or any brochures – please contact us.

  1. Handbuch 2 x V.24 Interface, PU 104 S2 1
    652.3812 - Handbook and Service Manual (German).
    Rohde & Schwarz. April 1986—April 1987.

  2. 80186, High-integration 16-bit microprocessor
    Intel 1982-1995.

  3. MB8464A Static Random Access Memory with Data Retention Mode, datasheet
    Fujutsu Microelectronics, 1978.

  4. D8259 Programmable Interrupt Controller, datasheet
    Digital Core Design, 1999-2007.

  5. MSM82C51 USART, datasheet
    OKI, January 1998.

  6. PM156, Monolothic JFET-Input Operational Amplifier, datasheet
    Analog Devices, date unknown.
  1. Manual kindly provided by Helmut Singer [2].

  1. Anonymous, PU-104 C1
    Information received June 2014.

  2. Helmut Singer, PU 104 S2 manual - THANKS !
    Received April 2018.
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Crypto Museum. Created: Monday 26 March 2018. Last changed: Wednesday, 11 April 2018 - 08:01 CET.
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