Robotron KC 85

The small computer the series KC 85/2-4 were from 1984 in the GDR from the state-owned VEB Microelectronics " Wilhelm Pieck " Mühlhausen from the combine microelectronics Erfurt in the models HC 900, KC 85/2, KC 85/3 and KC 85 / 4 built and were the most widely used computer in the GDR. The manufacturer first thought of the hobby and the private sector, but most computers for public education had to be rejected. Until shortly before the end of the GDR (about 1988), these computers were therefore difficult to obtain for individuals. Even the high price ( 4.300 M for the KC 85/3, 4.600 M for the KC 85/4 - later reduced to 2.150 M) made ​​sure that the " small computer " hardly found their way into private households.

  • 3.1 programming Languages
  • 3.2 Word Processing
  • 3.3 Games
  • 4.1 KC 85/5

History

In 1984, two home computers were introduced on the basis of the 8- bit microprocessor U880 ( Z80 ) in the GDR:

  • Z 9001, developed in the VEB Robotron measurement electronics "Otto Schön " Dresden, and
  • HC 900, developed in the microelectronics VEB Mühlhausen. This development was driven by Werner Domschke and was not covered by the East German government development. Despite some weaknesses, the development has led to some upsets in Robotron, because this machine in its basic equipment was full graphic.

The 1985 took place renaming of Z 9001 in KC 85/1, HC 900 in KC 85/2 was due to the change in the intended application, because the KCs should not be used as a home computer, but as a small computer in schools and other training institutions.

Hardware

Basic unit

The system architecture of the HC 900 was far from perfect: The realized with counter circuits monitor control was difficult to program. Essential system functions were implemented with PIOs (such as bank switching) and CTCs (cassette interface, blinking, sound ). The tone may have been effected by two CTC channels with downstream flip-flop. Extras such as blitter or sprites were missing. The operating system CAOS (Cassette Aided Operating System) and BASIC were quite comfortable, but slow. With the Muehlhaeuser original operating system the scrolling of the screen 0.6 seconds and clearing the screen took 1.75 seconds. This improved significantly with the KC 85/4. The KC 85/2-4 realized via additional modules some standard interfaces such as Centronics parallel printer, and serial interfaces ( such as RS232C and V.24). As of 1989, there were for the series floppy drives as an additional device, which was an own CP / M computer and the basic device used as a terminal.

HC 900 and KC 85/2

It was based on the 8-bit CPU U880 ( a Z80 - Clone) at 1.75 MHz ( 900 HC = KC 85/2 KC 85/3 ) and 1.773 ... MHz (KC 85/4 ) the processor clock. The typical use of Mulhouse computer was a KC 85/3 with 32 Kbytes of RAM (expandable with additional modules ), 16 Kbytes of ROM BASIC, attached cassette recorder for data storage and connection to a used as a monitor TV ( about UHF modulator, composite output or RGB output ). The KC 85/2, he had only 4 Kbytes ROM, lacked the ROM BASIC and lowercase letters. The KC 85/4 came with 128 KB RAM and enhanced graphics capabilities, but they were hardly exploited by the collapse of the GDR. All KC 85 from Mühlhausen were graphics capability; the screen resolution was 320 × 256 pixels. However, it was the " color resolution " considerably lower: for a pixel rectangle 4 × 8 pixels, it was only a foreground color (from 16 possible ) and a background color ( of 8 possible ) give. This restriction decreased during KC 85/4 on a line from 1 × 8 pixels, and in addition was a "real" color mode with 4 colors and without limitation can be turned on. Only at KC 85/4 accounted for the disturbing peculiarity of Mühlhausen KC- series that memory accesses of the CPU caused the screen image memory disorders.

KC 85/3

The expansion of the KC 85/3 were:

  • Now instead of 4 Kbytes ROM he had 16K ROM
  • Integrated BASIC interpreter (approx. 10.5 KByte)
  • Extended operating system CAOS 3.1 with commands such as DISPLAY, KEY and KEYLIST (about 4.5 KByte)
  • Uppercase and lowercase letters ( ASCII 00 .. 7F) in the ROM available
  • Piezo buzzer

KC 85/4

The major extensions of the KC 85/4 were:

  • Extension of the internal RAM of 32 KB to 128 KB
  • Other organization of the screen memory (so that at the hardware level incompatible with KC 85/2 and KC 85/3 )
  • Modification of the processor clock of 1.75 MHz 1.7734475 MHz to produce the system clock such as the chrominance signal with the same quartz
  • Access to screen memory without image distortion
  • Ordinary debouncing the reset button
  • Change the keyboard jack of 3.5mm jack to DIN
  • Larger text characters (upper case 7 lines instead of 6 rows high)

The biggest change was the extension to KC 85/2 and KC 85/3 incompatible, the screen memory organization:

  • Instead of one bank of 16 KByte 4 banks were each 16 KByte available.
  • The 4 banks gave 2 screens, could be switched between.
  • For each side of the screen ever 2 banks were used.
  • There was a 16-color mode in which the pixels in a bank and the other bank was on the front and background color for 8 horizontal pixels.
  • There was a four -color mode, in the stand in two banks, each with 1 bit corresponding to a permitted along the selection of four colors.
  • The organization of the screen memory was much easier: 256 bytes in video memory described a screen column of 8x256 pixels.
  • Diode socket dual-channel, constant- level
  • RGB output channel, volume control
  • Expansion Interface ( computer bus )
  • Diode socket for recorder
  • RGB and CVBS
  • Keyboard connector
  • Gross about 1200 baud
  • Net about 1,000 baud
  • Logic 0: Full wave 2400Hz
  • Logic 1: Full wave 1200Hz
  • Separator: Full wave 600 Hz

Expansion modules

There were a variety of expansion modules for the KC 85/2-4.

Recognize you could see the modules by reading from I / O port xx80, where xx is the number of the module slot. In the base - unit D001 module slots were 08 and 0C available. In an extension of essays D002 four additional slots were available (10, 14, 18 and 1C, switchable to other addresses).

By reading from the port xx80 gave the " Strukturbyte " said module identifier:

  • E7: M010 ADU ( 1 8 - bit A / D converter C570C with four switchable inputs ) - Schematic
  • EE: M003 V24 ( 2 serial ports )
  • EF: M001 Digital In / Out ( 16 parallel inputs / outputs as well as CTC connections)
  • F4: M022 16K RAM is automatically set to address 4000 during a cold start
  • F6: M011 64 Kbytes of RAM
  • Q7: M025 8 Kbytes User PROM
  • F8: 16 KB User PROM
  • FB: M027 Development ( Editor assembler debugger)
  • FC: M006 BASIC interpreter for the KC 85/2
  • FF: no module or module untagged
  • And many more. About this list.

Therefore, a certain degree of plug and play was realized.

  • Bit 0 activated normally a module, that is, the actual blocks ( RAM, ROM, or peripherals ) to be addressed
  • Bit 1 activated typing on a module (applies only to RAM modules ),
  • The high order bits usually put the base address or the rotation of the addresses fixed ( 16 KB, 64 KB ).

Papers

  • Housing attachment Busdriver D002 with its own power supply could accommodate a further 4 per appliance add-on modules.
  • Floppy Disk based D004 with its own power supply, contained a UA880 CPU with 4 MHz system clock and 64 Kbytes of RAM and could be up to four 800 - Kbyte floppy drives (Floppy Disk Drive, near the top ) operate. Actually, the D004 is a full CP / M machines, the only input / output via the base unit D001, which served as a terminal quasi transacted, ( there were also a mode in which the CAOS in KC the D004 just as fast mass storage used ).

Monitors

As a monitor often came the black and white TV Junost 402B used. The unit had only one antenna input. The picture quality was very moderate, letters were provided with disturbing ghosting.

About a connector on the back further signals were available:

  • CVBS
  • RGB composite sync
  • Mono sound, a mixture of the two Rechtecktongeneratoren, with common 16 - or 32- step volume influencing

They allowed the connecting TV with composite input (which is a medium quality enabled ) or RGB input. Since most televisions such inputs but did not have, you had to

  • Be satisfied with the RF input
  • Or on some devices was an extension possible ( built-in module ), eg in the RFT COLORMAT 4001 or robotron RC 6073
  • From the beginning of 1989 appeared the first devices with RGB input: RFT Color 40, robotron RC 9140
  • Principle is the connection of analog RGB monitor ( Commodore 1084S ) possible if the composite sync support or you HSYNC / VSYNC picks from the motherboard.

Mass storage

For mass storage produced cassette recorder of the brand Geracord GC 6000, GC 6010 or GC 6020 mainly came cassette players, especially in the VEB Elektronik Gera used. It was important especially the easy access to the azimuth adjustment screw.

Although the recording frequencies of 600 Hz to 2,400 Hz were quite low (you can transmit the signal over the telephone), the azimuth adjustment of different equipment was often quite different. Another problem was the drop-out rate of cartridges from the VEB ORWO Wolfen.

There were several approaches to speed this up:

  • Different turbocharger, partly as a pure software solution, partly as a hardware solution
  • Communication via V.24 with computers, the other mass storage had ( up to 57600 bps)
  • Connecting a floppy disk drive

Software

Programming languages

The KC 85/2-4 was in machine language, and (before the KC of cassette only with an additional module or RAM -BASIC 85/3 ) can also be programmed with a BASIC dialect that was much richer than about the BASIC in C64. Unlike most home computers, the system always started with the operating system CAOS (rather a better monitor); BASIC had to be explicitly called from this monitor, if it was ever available in ROM. The monitor commands could be easily extended by assembler programmers.

More, but less common programming languages ​​for small computers were Pascal and Forth. In the last years of the GDR a floppy adapter for this computer was built. This could then also CP / M ( Mulhouses name for it: " MicroDOS " ) and software are used for this.

Also for the KC 85/2-4 there was the BASICODE programming language. She is a compatible for a number of computers BASIC dialect, with programs for BASICODE were also broadcast on the radio.

Word processing

There were essentially two word processing programs available

  • Tex or: Worked with a 40x32 character screen and 8x8 pixel characters
  • Wordpro ​​: Worked with a 80x32 character screen and 4x8 pixel characters

Games

Essentially, there were two categories of games:

  • Games written in BASIC Often the character table has been redefined to allow the necessary graphics output in a usable speed.
  • More complex and faster games

Hobby projects around the KC 85/2-4

Popular DIY Projects were / are:

  • Port to a different keyboard
  • RAM disk
  • Interface Modules
  • Text systems
  • Connection of electronic typewriters as keyboards and printers (for example, Erika Typenradschreibmaschine S3004, 3005, 3006, 3015 and 3016 )
  • Connecting a 3.5 "floppy drive
  • Use a hard disk by means of GIDE interface
  • Scanner module M051
  • Network / USB module M052

The CAOS operating system regularly undergoes further development. Also there for the one supplied with the disk expansion CP / M newly developed versions. In addition, there were model attempts to implement solutions for control tasks (Programmable Logic Controller, PLC) for teaching purposes with the small computers. On the Breakpoint 2009, the KC 85/4 was used for a demo.

KC 85/5

The circuit board of the KC 85/4 was already preparing time of manufacturing for the use of more powerful types of memory. The use of these memory but was not realized until the series by the manufacturer setting. The built-in 64Kbit DRAMs can be easily replaced with 256Kbit types but thus. The CAOS and BASIC ROMs can be replaced by larger types with more advanced versions of the program without further changes are needed to the original hardware. Such an upgraded KC 85/4 is commonly drawn as KC 85/5.

Miscellaneous

  • Schemes: The diagrams were disclosed, which led to numerous additional circuits and programs. Especially the magazine " Amateur radio " the minicomputer accepted. She published circuits, listings and information about computer clubs. Other circuits and notes published in the journals " Practic " and "radio tv electronics ".
  • Thermal problems: The KC 85/2-4 had no fan. Summery room temperatures or contacted modules with increased electricity demand could overload the power supply of the computer temporarily. The system worked then unstable.
  • Reset to First: by a feature in the ROM of the KC 85/3 it was possible to RESET, to delete the main memory. Since this feature was based on a single bit (bit 7 of (IX 7), wherein IX was not initialized before the query ), the main memory in case of crash has often been deleted inadvertently.
  • Reset the Second: Because they forgot the ROM to initialize the stack pointer before calling the first sub- function, one could intercept the reset in a prepared stack pointer. However, you then could no longer use the subroutine stack of the CPU for the commands POP / PUSH / CALL / RET and interrupts.
  • Printer: Graphics-capable dot matrix printers were produced in the GDR, though, were on free trade but hardly available. Most copies were exported to the Federal Republic of Germany and sold there under the brand - source privilege. The also built in the GDR electronic Typenradschreibmaschinen Erika S3004, 3005, 3006, 3015 and 3016 could also be used as a printer. Through insistence programming ('.' And a lot of micro-steps were involved ) were also able to keep the graphics are printed.
  • The RF signal reception of FM stations was massively disrupted in the vicinity of the computer. Many functions generated characteristic disturbances (Screen Delete, View menu, screen scroll ).
  • Rem: In the broadcast of the GDR there was a popular computer program " Rem ". In addition to programming courses ( " Basic Intermediate " ) and tips and tricks so special was the fact that was broadcast over the airwaves software. The bits and bytes have been converted using the frequency modulation and pulse modulation in audible noise, which could be recorded by tape recorder and later downloaded to the KC.

More small computer from the GDR

  • Z 9001 or KC 85/1 and Z 9002 or KC 87: The KC 85/1 (identical with Z 9001 ) was developed and built by Robotron with the experience of proven themselves in the A 5120 K 1520 system. He had up to the 2.5 MHz processor, the BASIC dialect and the format for data storage on tapes little in common with the Mulhouse KCs. The KC 87 was an improved KC 85/1 with BASIC in ROM. These computers were also available with color option with an RGB output, but they offered no pixel graphics, only text -mode pseudo- graphics. The keyboard was installed in the base unit and consisted of tiny buttons with typewriter- like distance, which was very cumbersome to use.
  • Z1013: kit ( RAM Basic, Assembler, flat keypad, connector for black and white television, plug-ins )
  • LC80 ( LC learning computer ) single-board computer, only machine language, only with calculator keypad and 7-segment LED
  • POLY880: Learning computer for use as a learning machine in general education schools
  • KC compact: The gift for the 40th birthday Republic, very small numbers, CPC clones; came up with a neat, integrated into the housing keyboard, case and keyboard (but not the electronics) were taken from the BIC, A 5105, since the end of 1989 for this purpose existing in Robotron assets were sold for one million marks to Mühlhausen. Later basing comfort keyboard D005 for the KC 85/4 were offered by Mühlhausen.
Volkseigener Betrieb Sprite (computer graphics) Clone (computing) ROM cartridge Dropout (communications) Machine code monitor Forth (programming language) Breakpoint (demo party) Listing (computer) Switch#Contact bounce Robotron Z1013
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