View source for KC 85

{{Short description|Microcomputers made in East Germany, 1984–1990}}
{{More citations needed|date=November 2022}}
{{Infobox information appliance
| name = KC 85
| title = 
| aka = "Kleincomputer"
| image = KC85-4.jpg
| caption = KC 85/4
| developer = 
| manufacturer = [[Kombinat Mikroelektronik Erfurt|VEB Mikroelektronik]] "[[Wilhelm Pieck]]" [[Mühlhausen]]
| family = 
| type = [[Microcomputer]]
| generation = 
| releasedate = HC&nbsp;900: Q2 1984<br /> KC&nbsp;85/2: Q2 1985<br /> KC&nbsp;85/3: Q2 1986<br /> KC&nbsp;85/4: Q2 1988<ref name="kc85 timeline">{{cite web|title=KC 85 Timeline (German)|url=http://www.mpm-kc85.de/html/zeitskala.htm|website=mpm-kc85.de|access-date=11 February 2023}}</ref>
| lifespan =  6 years
| price = KC&nbsp;85/3: 1700 [[East German mark|M]]<ref name="heimcomputer_de_kc85_3">heimcomputer.de: [http://www.heimcomputer.de/comp/kc85_3.html ''RFT KC 85/3''] queried on 6 March 2023.</ref><br /> KC&nbsp;85/4: 4100 M<ref name="heimcomputer_de_kc85_4">heimcomputer.de: [http://www.heimcomputer.de/comp/kc85_4.html ''RFT KC 85/4''] queried on 6 March 2023.</ref>
| discontinued = HC&nbsp;900: 1985<br /> KC&nbsp;85/2: 1986<br /> KC&nbsp;85/3: 1988<br /> KC&nbsp;85/4: Q3 1990<ref name="kc85 timeline" />
| unitssold = ~45.000<ref name="kcs_muehlhausen">{{cite web|title=Kleincomputer aus Mühlhausen (German)|url=https://www.robotrontechnik.de/html/computer/kc_muehlhausen.htm|website=robotrontechnik.de|access-date=10 March 2023}}</ref>
| unitsshipped = 
| media = [[Cassette tape]], [[floppy disk]], expansion modules
| os = CAOS [[:de:Cassette Aided Operation System|[de]]] (4 KB)<br />KC 85/3 and KC 85/4: ''KC-BASIC'' [[:de:KC-BASIC|[de]]] interpreter in [[Read-only memory|ROM]]
| power = 25 W
| soc = 
| cpu = [[U880]] ([[Zilog Z80]] clone)
| memory = 32 KB <br />KC 85/4: 64+64 KB
| RAMtype = [[Dynamic random-access memory|DRAM]]
| storage = 
| memory card = 
| display = 320×256 pixels, per 4 × 8 pixels: 1 of 16 foreground and 1 of 8 background colors <br />KC 85/4: more colors
| graphics = series [[7400-series integrated circuits|7400]] ICs
| sound = 2x square wave, 8 volumes, 6 octaves <br />KC 85/3 and KC 85/4: [[Buzzer]]
| input = 
| controllers = 
| camera = 
| touchpad = 
| connectivity = 
| platform = [[VEB Robotron#K 1520_bus_standard|K 1520 bus]]
| service = 
| dimensions = 38.5 cm × 27.0 cm × 7.7 cm<br />(15,2 in x 10.6 in x 2.8 in)
| weight = 4,1 kg
| topgame = 
| compatibility = 
| predecessor = 
| successor = 
| related = 
| website = <!--{{URL|example.org}}-->
}}
The '''KC 85'''<ref>{{Cite web |title=The KC85 Computers |url=https://floooh.github.io/virtualkc/p010_kc85.html |access-date=2022-11-24 |website=floooh.github.io}}</ref> ('KC' meaning "Kleincomputer", or "small computer") were models of [[microcomputer]]s ('''KC 85/2''', '''KC 85/3''' and '''KC 85/4''') built in [[East Germany]] by [[Kombinat Mikroelektronik Erfurt|VEB Mikroelektronik]] "[[Wilhelm Pieck]]" [[Mühlhausen]]. The first model in the series, the '''HC 900''', originally designed as a [[home computer]] and introduced in 1984, was renamed to KC 85/2 in 1985 to de-emphasize its use as consumer good.<ref name="kcs_gdr">{{cite web |title=Die Kleincomputer der DDR |url=http://www.robotron-net.de/kc85xx.html |website=robotron-net.de |access-date=10 March 2023}}</ref><ref>{{Cite web |title=www.robotrontechnik.de - Die Geschichte der Computertechnik der DDR |url=https://www.robotrontechnik.de/index.htm?/html/computer/kc.htm |access-date=2022-11-24 |website=www.robotrontechnik.de}}</ref><ref>{{Cite book |last=Gruppe |first=Bcher |url=https://books.google.com/books?id=GFRhcAAACAAJ |title=Kombinat Mikroelektronik: Kleincomputer Kc 85{{!}}2-4, Kombinat Mikroelektronik Erfurt, Schachcomputer in Der Ddr, U61000, Kc Compact, Mme U80701 |date=July 2010 |publisher=General Books LLC |isbn=978-1-159-10174-9 |language=de}}</ref>

Despite similar names, the KC 85 computers were not directly related to the [[Robotron KC 87|KC 87]] series produced by [[VEB Robotron]]-Meßelektronik "[[Otto Schön]]" [[Dresden]].<ref>{{Cite web |title=www.robotrontechnik.de - Die Geschichte der Computertechnik der DDR |url=https://www.robotrontechnik.de/index.htm?/html/computer/kc.htm |access-date=2022-11-24 |website=www.robotrontechnik.de}}</ref><ref>{{Cite web |title=KC 85/1 - Z 9001 Robotron |url=https://www.old-computers.com/museum/computer.asp?st=1&c=599 |access-date=2022-11-24 |website=www.old-computers.com}}</ref>

The availability of the KC 85 series for private customers was very limited. The computers were mostly used at educational institutions, organizations, and enterprises.

==Technical information==
They were based on the [[U880]] [[Central processing unit|CPU]] (an East German clone of the [[Zilog Z80|Z80]]), with clock speeds of 1.75&nbsp;MHz (KC 85/2, KC 85/3) and 1.77&nbsp;MHz (KC 85/4). 

Unlike the [[Pravetz series 8]] personal computers, manufactured in [[Bulgaria]], which were equipped with dedicated displays, floppy disks and quality keyboards, the entire KC series used TV sets for display purposes. Connectors provided were TV-out via [[coaxial cable]], [[composite video]], [[Component video#RGB analog component video|RGB video]]. Generic tape recorders was used for data storage. The KC 85 used a separate keyboard driven by a remote control IC.

The KC 85/2 was the first computer made in Mühlhausen and had only font ROMs for capital letters, and no [[BASIC]] in ROM. Later, the KC 85/3 was introduced and this one had a ''KC-BASIC'' [[:de:KC-BASIC|[de]]] interpreter in [[Read-only memory|ROM]], freeing the user from having to load it from a cassette every time. Both systems typically had 16&nbsp;KB of free RAM, but could be expanded with add-on modules. The module sockets feature prominently on photos, as they occupy the upper 50% of the casing.
The KC 85/4 had 64&nbsp;KB of RAM, not counting the video ram of more than 40&nbsp;KB, and better graphics capabilities. In fact, the KC 85/2 and KC 85/3 were practically indistinguishable in board design except for a different ROM and an internal [[piezoelectric speaker|piezo speaker]]. The KC 85/4 board was redesigned, but featured the same digital-to-analog video [[printed circuit board|PCB]] as the previous generation.

[[File:KC85-4 CAOS.gif|thumb|KC85-4 after power on]]

All KC-series computers from Mühlhausen were capable of displaying graphics at a resolution of 320×256 pixels. The video ram layout was awkwardly split into a 256x256 portion and a 64x256 portion to avoid a time-consuming multiplication with 40 when addressing video memory. On the KC85/4 the video ram layout was changed in a backwards-incompatible manner to 40 columns of 256 bytes and the bytes in one column were put into consecutive memory addresses. The [[kernel (operating system)|kernel]] interface was of course kept as-is and software that relied on it could continue running unchanged. The color possibilities were limited in the typical color-cell fashion: each 4×8-pixel cell had a single foreground (out of 16) and background color (out of 8, slightly darker than foreground equivalents). 
This limitation was brought down to 1×8 on the KC 85/4 (the color cells on both the KC85/3 and KC85/4 were thus quite small compared to contemporary systems). The KC85/4 also featured a special 4-color (black, white, red, cyan) mode which could color every pixel independently. The colors were not paletted. There was no "text mode", everything had to be painted; this combined with the video RAM layout described above and ROM code made the KC 85/2-3 rather slow at printing and scrolling (improved very much on KC 85/4). There were no [[blitter]]s, sprites or hardware scrolling, not a single [[hardware register]] with which to influence the display drawing process, the sole exception being the blink attribute, whose frequency could be tuned by programming the dedicated CTC register and which required no CPU assistance. The KC85/4 added one bit to select which of the two [[framebuffer|buffers]] to display and one bit to switch between high color (using color cells) and high color-resolution mode (using the color RAM as a second [[bit plane]]). The video subsystem was developed in-house and implemented entirely with a few dozen series [[7400-series integrated circuits|7400]] ICs. With the KC 85/2 and KC 85/3 CPU access to video memory would interfere with screen redraw and cause visual distortions as pixel data could not be read from [[VRAM]] and the previously loaded strip of 8 pixels was simply drawn again. This issue was fixed in the KC 85/4 too - one video period of 8 horizontal pixels is divided evenly into 3 phases: (1) an 8 bit wide CPU access (r/w), (2) fetch 8 bits of pixel data and (3) fetch 8 bits of color data. The KC 85/4 was also the first capable of switching between 2 independent locations in video ram, allowing double buffering.

Sound and tape output was implemented by a [[Zilog_Z80#Compatible_peripherals|CTC IC]] driving flipflops to generate [[Square wave (waveform)|square wave]]s. A zero was represented by one period of a 2400&nbsp;Hz tone, a one by a 1200&nbsp;Hz tone. There was also a sync tone of 600&nbsp;Hz prefixing each byte. The signal from the tape was read back, passed through a [[band pass filter]] and an interrupt would be generated each time the audio signal crossed the 0&nbsp;V base line.

Data was stored on tape in blocks of 128 byte. Each block was prefixed by brief silence and a
series of 1 bits. Approximately 8000 (7 seconds officially, but it could be shorter) for the first block and 160 (133&nbsp;msec) for each
subsequent block. Following that was the 1 byte block number, 128 data bytes and 1 byte [[checksum]].
The tape could be rewound in case a block was not read correctly and loading would continue at
that block offset. The first block of the file contained [[metadata]]: filename, file type, load address,
entry point address and so forth.

Memory [[bank-switching]] was common since the total address space was only 64&nbsp;KB. When running Mühlhausen's BASIC, the video RAM (at 0x8000) was banked in only during video operations, thus the maximum BASIC free RAM was about 47&nbsp;KB instead of 32&nbsp;KB. The module extension system also used bank-switching and made it theoretically possible to extend to [[megabytes]] of RAM (even more modules could be used by adding expansion devices, yielding sort of a tower), however neither BASIC nor most of the applications were prepared to use this as free space.

The keyboard of the KC 85/2-4 was based on the U807D, a clone of the [[Mullard]] SAB3021 used in TV infrared remote controls. The U807D scanned the 63 regular keys with its 8&nbsp;+&nbsp;8 drive/sense pins and produced a 7 bit [[pulse width]] modulated signal (0: 5&nbsp;ms, 1: 7&nbsp;ms). The main computer would detect the presence of pulse delineating bursts (150&nbsp;us) and generate [[interrupts]]. The main CPU would thus be interrupted 7 times for each keystroke and could measure the time between the interrupts to recover the serial [[data word]]. A special shift key made the U807D produce keycodes 64-127. To the computer the keyboard appeared as a device with 126 keys. Transmission occurred through the same wire that provided power to the keyboard. Since the keyboard was connected to the 12V [[voltage rail]] through a [[resistor]], an increase in current consumption could be measured between the resistor and the cable as a voltage drop, inside the main computer. The keyboard just had to set a digital output low and shunt some additional current to ground. All the while the keyboard supply voltage was kept stable by a simple 9V [[zener diode]], with which the controller IC was connected in parallel and if it remained within a certain window of current usage, 9V is what it would see.

There was a single 8867&nbsp;kHz crystal oscillating at twice the [[PAL]] [[Chrominance#Television standards|chrominance]] frequency and a divide-by-10, multiply-by-16 [[phase-locked loop]] was used to derive a 14.2&nbsp;MHz clock from which the pixel clock (7.1&nbsp;MHz) and processor clock (1.77&nbsp;MHz) was derived by division by 2 and 8, respectively (KC85/2, KC85/3 and KC85/4 used the same circuit for this purpose, since the digital to analog video conversion PCB where the clock generation was situated did not change between revisions). There was still a slight difference in effective clock rate, the KC85/2 and KC85/3 skipped a few [[CPU cycle]]s at the end of each [[scanline]], to provide in a simple manner to the entire system the illusion of a horizontal resolution (including blanking) divisible by 8, the KC85/4 did not. None of the revisions had provisions for either [[vertical blank interrupt]]s or [[horizontal blank interrupt]]s.

The wiring diagrams are freely available and there were also a lot of different (and often home-made) schemes and hardware parts. Various magazines published programs and hardware diagrams and also instructions on how to build them.

{{clear}}
<gallery>
File:KC85-2-1.jpg|KC 85/2
File:Kc85-3.jpg|KC 85/3 with two expansion cartridges installed: a 64&nbsp;KB [[RAM]] module and a [[parallel port]]
File:KC85-2-5.jpg|Mainboard of the KC 85/2
File:KC85-3-5.jpg|Mainboard of the KC 85/3
File:Radebeul-DDR-Museum-Kleincomputer-KC85-I9365-pCOSt-12-08-2012-1346.jpg|KC 85/3 (black) with ''GC6020'' floppy disk expansion (gray), manuals, cassette tape, tape deck and expansion modules
File:Bundesarchiv_Bild_183-1989-0508-014,_Dresden,_Softwarebibliothek,_Nutzerin.jpg|KC 85 used in a software library (1989)
</gallery>

==Programming languages==
The KC 85 could be programmed in [[assembly language]] and BASIC (the KC 85/2 had to load BASIC from tape), but it was possible to use various modules (sold by VEB Mikroelektronik Mühlhausen) or load software from tape, thus allowing programming in [[Forth (programming language)|Forth]] and [[Pascal (programming language)|Pascal]]. The [[operating system]] was CAOS ("Cassette Aided Operating System"). It was a simple monitor where one could run different "system services" like LOAD (load a program), JUMP (into extension module ROM), MODIFY (memory cells) or BASIC (if it had been built into the ROM or had been loaded from tape). New commands could be added to the menu by magic numbers (standard: <code>7F 7F 'commandname' 01</code>) anywhere in the memory space.

In the last years of [[East Germany|the GDR]], a floppy attachment ("tower"-style, too) was produced. It featured a 4&nbsp;[[MHz]] CPU and a 5¼" [[Floppy disk|Floppy drive]] (you could have up to four of them). These (literally: the U 880 A in the attachment did) were able to run [[CP/M]], which was called [[MicroDOS]]. (One had to JUMP from the base system to the floppy system and boot from a floppy—another CAOS or MicroDOS). There was also a disk extension mode for CAOS.

==Games==

There are 10 commercial cassettes for the KC 85.<ref>{{cite web
 |url=https://www.mpm-kc85.de/html/Kassetten.htm
 |title=Übersicht – KC85 Kassetten
 |website=mpm-kc85.de
 |language=de
 |access-date=15 September 2025
}}</ref>

{| class="wikitable sortable mw-collapsible plainrowheaders" style="width:50%; font-size:95%;" id="softwarelist"
!rowspan="1"|Title
!rowspan="1"|Release year
!colspan="1"|Publisher
|-
|Demo 85/4 (VORSTELL/4, OTHELLO)
| align="right" |1988
|VEB Mikroelektronik
|-
|Spiele 1 (PILZE, STADT, LABY, RENNEN, LOCH, PERLEN , PINGUIN)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 2 ( SCHIFFE, SANDBURG, ALI, ROSCH, ANGELN, LANDER, SKI)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 3 (GOWA, COCKPIT, ORBIT, ENTEN)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 4 (CLUB-X)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 5 (PURSUI/3, PURSUI/4, CAVE/3, CAVE/4)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 6 (DELIRIO, PENGO/3, PENGO/4)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 7 (DIGGER/3, DIGGER/4, 4 GEWINNT)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spiele 8 (GATECRASHER, HOUSE/3, HOUSE/4)
| align="right" |1986
|VEB Mikroelektronik
|-
|Spielprogramme II (SCHACH)
| align="right" |1986
|VEB Mikroelektronik
|}

==Hobby projects==
There were a lot of different projects for the KC 85:
*a new keyboard (The original being extremely poorly manufactured)
*[[RAM disk]]
*interfaces ([[RS-232|V.24]] and others)
*text systems; ''WordPro'' actually featured 80 characters per line mode (4&nbsp;×&nbsp;8 font)
*connection to electronic typewriters (like the GDR-product "Erika S 3004") as keyboard and printer (but dot matrix emulation was very slow)
*programming language [[BASICODE]] (a special [[BASIC dialect]]); BASICODE-programs were even broadcast by radio

== See also ==
* [[Robotron Z1013|Robotron Z 1013]] – A mostly compatible hobbyist kit, available even to private consumers via written order, waiting of one year and then self-pickup from factory outlet.
* [[Robotron KC 87]] – A series of mostly compatible microcomputers from a different manufacturer.
* [[Amstrad CPC#KC compact|KC compact]] – The only pre-assembled [[home computer]] made in the GDR aimed at private consumers; not compatible to any of the other KC systems.

==References==
{{Reflist}}

==External links==
* [http://www.robotron-net.de robotron-net.de - Homepage for GDR-Kleincomputer] {{in lang|de}}
* [http://www.iee.et.tu-dresden.de/~kc-club/ tu-dresden.de - KC-Club Homepage] {{Webarchive|url=https://web.archive.org/web/20041202173928/http://www.iee.et.tu-dresden.de/~kc-club/ |date=2004-12-02 }} {{in lang|de}} Active until around 2003. Provides manuals as download.
* [https://www.kc85-museum.de/ kc85-museum.de] {{in lang|de}}
* [https://www.robotrontechnik.de/html/computer/kc.htm robotrontechnik.de - KC 85] {{in lang|de}}
* [http://www.mpm-kc85.com/ mpm-kc85.com - KC85/4 - The modular monster] {{in lang|en|fr}}
* [http://www.mpm-kc85.de/ mpm-kc85.de - KC85/4 System Aufbau Bedienung] {{in lang|de}}
* [http://www.jens-mueller.org/jkcemu/ jens-mueller.org - JKCEMU, a KC emulator written in Java] {{in lang|de}}
* [https://www.sax.de/~zander/kc85/kc85_bw.html sax.de/~zander - Manuals for KC85/2, KC85/3, KC85/4] {{in lang|de}}

{{DEFAULTSORT:Kc 85}}
[[Category:Z80-based home computers]]
[[Category:Goods manufactured in East Germany]]
[[Category:Science and technology in East Germany]]
[[Category:Computers designed in Germany]]
[[Category:Computer-related introductions in 1984]]