Data communication; period 1978 - 1983

CDC 2551 data communication processor

The period 1979-1980 showed a fast expansion of the number of asynchronous terminals of the Newbury brand. During the selection of the standard Laboratory terminal, the users' commission took into account many aspects like function keys, screen color (green) and the noise production of the terminal.
The CDC mainframes' CDC 6671 data communication controller was replaced by a CDC 2551, a mini-computer with 96 Kwords, 16 bits. This system had 32 slots for Communication Line Adapter boards (CLA’s). The Laboratory had four synchronous CLA’s (2 lines each) and 28 asynchronous CLA’s (2 lines each) boards. After the installation, the 110/300 baud dial-up modems refused to do their work. After using an electronic scope - system programmers had to know about many different perks! - the problem became clear. The very fast processor sampled the data communication signals much faster than before. The ring-signal (ring-indicator) of the ENA-modems had many spikes causing the 2551 to switch off the lines. Modifying the modem by adding large condensers stabilising the modem solved the problems.

Note that the 2550 was derived from the Cyber 18, which was actually the semiconductor version of what had originally been the discrete-transistor CDC 1700. The CDC team working on the 2550 started talking about how they would decide on a name. One of them pointed out that they had crammed so much extra stuff in it that it was "half again better than a 1700". This resulted in the type number 2550 as it equals 1700 x 1.5. (with special thanks to Tim Roberts who provided this inside infromation)

The system program running in the 2551 was very complex. It consisted of about 700 pages of code written in a Pascal-like programming language, several hundreds of pages microcode (state tables) and assembler code. As the CYBER usually used 6-bit code, the PP’s used 12 bits code and the 2551 used 16-bits code, very complex cross compilations were required to obtain a byte of 2551 executable code. At the end, the 2551 was started by a PP-program that loaded the 16-bit based executable code. A simple compilation could last three to four hours at the CYBER 74.

In the beginning of 1981, we tried to upgrade to a new version of the total interactive operating system (INTERCOM). The upgrade from INTERCOM 4 to version 5 did not went smoothly. The synchronous links with the PDP’s minicomputers at the LEOK, PML and IZF did not work. The MUX200 emulated "card jobs" gave at their side the message "slipped card". However, at our Laboratory side, we could not see or even find the text of that message. No card jobs were found either. Even additional trace code did not show irregularities. Reasons enough to rent a data analyser. And yes, after studying the protocol blocks of a batch job on the CDC 734 and a batch job of the LEOK, the cause of the problem became clear. An end-of-record card required the indication (punches) of two bytes to signal the record level in card column 1 (Escape E4). The UT-200-emulation code in the PDP minicomputer padded the Esc-E4 with 78 blanks. Under INTERCOM 4 the rest of the card was ignored, thus no problem. Intercom 5, however, was much stricter in reading 'cards' and required 79 additional card columns. The emulator generated already for years one card column less. PML, maintainer of the emulation code, made a small change in the PDP-code in order to solve this problem.

DATUS 5810 port selector

To reduce the need for expensive asynchronous ports in the 2551 and to cope with the fast growing need for asynchronous connectivity to the CYBER, but also to reach other systems from the same terminal, the computer group acquired at the end of 1982/ early 1983 a DATUS 5810 port selector with 32 ports. This DATUS port selector worked like a PABX system for data communication interconnections. At a workplace, one could setup a direct connection with the CYBER, the Datanet-1 packet assembly/dis-assembly (PAD) modem or choose a dial-out modem. The DATUS was expanded a couple of times with tenfolds of in- and outgoing lines. The DATUS was in use until 1993. After that time, only the dial-up security module (DUS) was kept in production until the beginning of 1995.

Single Board Computers (iSBC’s)

Many graduated students, who had to fulfill their military duty at the Laboratory, were involved to develop code for the Intel Single Board Computers (iSBC’s) with 8085/85 microprocessors. These iSBC's were used as interface/controller for special I/O-equipment that required connection to the CYBER 74 via asynchronous lines. Examples: the magnetic cassette reader, the papertape reader and papertape puncher, a PROM-programmer and a photo-plotter (belonging to the Synthetic Apparture Radar-group).
All "data communication" software was developed by the Laboratory. Much later, the controller was changed and connected to the Data conversion station, a DEC system.

To demonstrate the proper working of the photo plotter, several members of the Computer group developed an unusual test. At that time, computer experts collected so-called "printer pictures". Those were pictures being built-up from repeatedly overprinted lines. Specific combinations of overprinted characters gave another impression of the "grey value". The new photo plotter was reason enough to plot one of the "pin-up girl" printer pictures. That required some manipulation of the grey-values. That was not enough. Almost without visible discontinuity, a female picture was constructed having four breasts. After calculation of the grey values this "computer genetic-manipulated" beaty was given a photo-realistic reality.

PDP 11/34 Data conversion station (DCS)

To couple and drive "CYBER"-strange equipment, the PDP 11/34 Dataconversion station (DCS) was installed in 1981. This DCS was the replacement of the very old Cyber 18-17. The DCS supported nine data streams, two for input to the Cyber 74 and seven for driving output equipment. These streams were: papertape read (Facit 4020), papertape punch (Facit 4070), printing on the DAISY-wheel printer and the C.ITOH-matrix printer, coontrolling the Calcomp 1051 plotter (May 1983), reading floppy-disks (14" LARGE ONE's!), reading magnetic data cassettes (Facit 4203), the Micro Development Station and data streams to/from the PDP 11/60 for exchanging graphical data.
The PDP 11/34 minicomputer operated under the RSX 11/M operating system, had 256 KB memory and two exchangable RL02-disks of 10.4 MB each. The total system costs were Dfl 200.000.

A Daisy wheel

The CYBER - DCS interconnection was based on the HASP-protocol. HASP (Houston Automatic Spooling Program) is a by IBM developed communication protocol for synchronous lines. HASP could drive multiple datastreams at the same time over the same line. After initial tests with data transports on basis of card- and printer images (columns and lines) the project leader read in March 1982, that HASP supported transparent streams as well. Once again, the Laboratory's Computer group detected a less tested corner of the INTERCOM system. As soon as the transparant buffers exceeded the (line printer limit) of 137 characters, the CDC 2551 restarted with a fatal error message. At the same time, all unsaved typed characters and command results were lost. Using another test sequence that tried to explore the data compression part of the transparent HASP protocol, the 2551 software went into a loop. Time for systematic tests and analysis of dumps and code. We finally figured out that a combination of two errors in the microcode resulted in the "eating" of memory buffers, causing the 2551 to become slower and slower. After solving these problems, we increased the transport of the information blocks to the highest limit allowed by the protocol (some Kbytes). As transparent HASP, supports a simple data compression mechanism, an effective line utilisation of over 100% could be achieved.

Micro Development Station (MDS)

The Elektronics development group started developing code for microprocessors. In the beginning of the eighties, they required support for developing microprocessor software. The Micro Development System (MDS), an INTEL MDS 231, was bought. It supported software development for the 8080, 8085/8086 and 2920 microprocessors. The compilers available on the MDS system were: PL/M, Fortran80 and Assembler.

To make effective and efficient use of this expensive system, it was decided to edit all programs on the CYBER 74. At the same time, all libraries and data was stored on the CYBER as well. The expensive and large CYBER 74 became a front-end for the Data conversion station, which in turn was a front-end for the MDS system. Command Control Language procedures (CCL) were developed to put jobs into the MDS-queue on the CYBER. Other procedures that could be called from within the MDS loaded files and libraries from the CYBER onto the MDS.

The TNO-special TAB 132/15 terminal

The requirements by the Laboratory for the "standard terminal" could not be fulfilled by any supplier on the market. The terminal had to support "on-screen" editing, like the old synchronous screens, and had to work as well with the CYBER, the PDP’s minicomputers and Data General computers. Long sequences of characters and function codes had to be saved under function keys, a "self-learning" mode and down-loading from the computer (content sensitive function keys) had to be possible.

Reason enough to obtain the source of the TAB 132/15 microcode and to write the feature code ourselves. The program was adapted by several microcode programmers and compiled on the MDS system. The localised version was baked into an EPROM and put into TAB 132/15 terminals.
The programming features of the new terminals introduced new security problems. Complete login-commands including the passwords could be found under the function keys.

MuseumWaalsdorp@tno.nl