MicroBee

MicroBee
Developer Applied Technology
Type Home computers
Release date February 1982
Introductory price A$399 in Kit Form
Discontinued 1990
Operating system MicroWorld BASIC
DGOS (David Griffiths Operating System)
CPU Zilog Z80 @ 2 MHz
Memory 16 kB or 32 kB
Graphics Synertek 6545 CRT controller for 64 × 16 characters (512 × 256 pixels)
Sound Monotonic sound generator & speaker, 2 octaves

MicroBee (Micro Bee) was a series of home computers by Applied Technology, later known as MicroBee Systems.

The original MicroBee computer was designed in Australia by a team including Owen Hill[1] and Matthew Starr. It was based on features available on the DG-Z80 and DG-640 S-100 cards developed by David Griffiths, TCT-PCG S-100 card developed by TCT Micro Design and MW6545 S-100 card developed by Dr John Wilmshurst. It was originally packaged as a two board unit, with the lower "main board" containing the keyboard, Zilog Z80 microprocessor, Synertek 6545 CRT controller, 2 kB of "screen" RAM, 2 kB of character ROM (128 characters) and 2 kB of Programmable Character Graphics (PCG) RAM (128 characters). Each byte in the screen RAM addressed a character in either the character ROM or PCG RAM. A second board, termed the "core board", contained the memory, and on later models also included a floppy disk controller.

Kit beginnings

The computer was conceived as a kit, with assembly instructions included in Your Computer magazine, in February 1982.[2] After a successful bid for the New South Wales Department of Education computer tender, the computer was repackaged in a two-tone beige and black case, and sold pre-built. The 16 kB ROM held the MicroWorld BASIC interpreter written by Matthew Starr and DGOS (David Griffiths Operating System) compatible System Monitor. In addition to the 16 kB ROM, there is additional ROM socket for optional programs such as WORDBEE (Word processor) or EDASM (a Z80 Editor/Assembler that was written by Ron Harris).[3]

Original MicroBees ran at a clock speed of 2 MHz, with a video dot clock of 12 MHz, which was sufficient to display 64 × 16 characters (512 × 256 pixels) on a modified television or composite monitor. The original machines were supplied with 16 or 32 kB of static RAM, and stored programs on cassette, using 300 or 1200 Baud encoding.

The IC model

The IC model was released in 1983, increasing the clock speed to 3.375 MHz, and allowing (through use of a 13.5 MHz video clock) display of 80 × 24 characters (640 × 264 pixels), again on a modified television or composite monitor. It also included a 4 kB "Telcom" terminal emulator ROM.

A complete MicroBee Computer-In-A-Book system.

Disk machines

A floppy disk based machine was also released in 1983. Early disk machines used 56 kB of static RAM, with a 4 kB BIOS ROM. They ran CP/M 2.2. The disk controller, based on the Western Digital WD1793 Floppy Disk Controller chip was contained in an add-on card that connected to the core board. The machines uses 5.25" floppy disks.

Dynamic RAM disk machines with 64 or 128 kB RAM followed soon after, with a WD2793 Floppy Disk Controller incorporated on the core board. Later disk machines used 3.5" floppy disks.

Colour

A colour machine was also released in 1983, called the "32K Personal Communicator". This added a second byte of RAM for each character position, allowing each character to have 2 colours. The foreground colour has 32 possible values (5 bits) and are determined by the contents of the 82S123 PROM located on the colour board. Not all foreground colours combinations are unique with only 26 being possible. The background colours were made up from the remaining 3 bits of the colour RAM byte (7 colours) and another 3 bits on a colour control port that controlled the RGB background intensity level. This allowed the intensity of each of the RGB colours to be set to full or half intensity but only 7 different values could be in effect at any one time and changing the intensity value would affect the entire display. The extra colour circuitry required an additional board mounted under the main board, with numerous messy connections to the main board.

The Premium, 256TC and Teleterm models released in 1986 incorporated colour on the main board and used a different colour design compared to the earlier model and was not compatible for the resultant colours that were produced but application and system software will work on either hardware designs. The later colour design was largely compatible with the Color Graphics Adapter used on the IBM PC where 4 bits were used for the foreground and another 4 bits for the background colours.

The B-ETI Serial Terminal

The B-ETI was a Microbee based serial terminal. It could emulate either an ADM-3A or Televideo 912 terminal. The display format was monochrome 80 × 24 and it supported communication at either 300 or 1200 baud. An advertisement for a "special introductory offer" with an asking price of A$275 appeared in the December 1983 issue of Electronics Today International magazine.[4]

Introduction, BETI Users Guide:

The BETI was designed as a low cost serial terminal operating at speeds of up to 4800 baud (1200 baud without handshaking). The BETI also provides optional automatic code conversion to and from the baudot 5 level code used for RTTY and TELEX applications.

Specifications:[5]

The Premium Series MicroBee

In 1985, a new mainboard was introduced. The resulting machine was called the "Premium Series" model. The new mainboard had 8 kB of screen RAM, 8 kB of "attribute" RAM (raising the possible number of PCG characters to 32 768), 8 kB of colour RAM, and up to 32 kB (16 kB installed) of PCG RAM. 16 kB PCG RAM was sufficient to allow full 512 × 256 bit mapped displays with a limited colour palette. These machines were typically sold with dual-floppy drives (or a 10 MB 'Winchester' disc) held in a monitor stand that connected to the main unit.

Physical coding for tape storage

Microbee 32K IC

MicroBee computers, at least MicroBee 32 use 300 or 1200 baud and conforms loosely to the "Kansas City" standard. A frequency of 1200 Hz means "1", 2400 Hz means "0". At 300 bit/s, one bit lasts 1000 µs, at 1200 bit/s, one bit lasts 250 µs.

The bit stream is stored as, Start bit - 0, LSB....MSB, 2 stop bits.

The wav2dat software converts audio data into Microbee files.

Books

A few books were written about the Microbee, including:

Games

Many memorable games were written for the Microbee, including:

As well, numerous adventure games were written, mainly in BASIC, plus educational software.[12][13]

Final versions

The final version of the MicroBee, released in 1987, was the 256TC. This increased the memory to 256 kB of dynamic RAM and had a new keyboard with numeric keypad. The computer had a built in 3.5" floppy disk drive supporting both 800 kB (DSDD) and 400 kB (SSDD) formats. Bundled software included "Videotex" a videotex terminal program, "Simply Write" (a word processor) and "Telcom" (a serial terminal emulator program).

MicroBee Systems also designed a PC clone, called the "Matilda", or 640TC, which ran an NEC V40 (see NEC V20 chip), and emulated the MicroBee CP/M systems in software.

An advanced next generation model code named "Gamma", based on the Motorola 68010 and two Zilog Z80 processors, was designed but never made it to the market.[14][15]

Relaunch

The Microbee brand has re-launched after almost 20 years with a limited edition (100 unit only) kit, the Premium Plus. The new version is still Z80 based with a dual processor architecture and some added enhancements such as floppy emulation of the SD memory card for instance. It still follows the original two board design.[16]

References

  1. ↑ Secret of project Granny Smith By Gordon Laing, July 12, 2005 - theage.com.au
  2. ↑ Microbee computer, From:Owen Hill Date:24 Aug 1998, Link list on Australian network policy and communications
  3. ↑ Graphic Word bee user's manual by Ron Harris and Gordon Rowell, Honeysoft, c1985., National Library of Australia
  4. ↑ B-ETI Advertisement. (December 1983). Electronics Today International, p. 51.
  5. ↑ "BETI Serial Terminal Operator's Guide", Microbee Technology.
  6. ↑ Burt, Robert; Ford, Peter T.; Ash Nallawalla (1983). Wildcards. Australia: BF&N Publishing. p. 100. ISBN 0949127000.
  7. ↑ Burt, Robert; Ford, Peter T; Ash Nallawalla (1983). Wildcards 2. Australia: BF&N Publishing. p. 120. ISBN 0949127019.
  8. ↑ Burt, Robert; Ford, Peter; Ash Nallawalla (1985). Wildcards 3. Melbourne: Pitman. p. 109. ISBN 0858962039.
  9. ↑ Burt, Robert; Ford, Peter; Ash Nallawalla (1985). Wildcards 4. Melbourne: Pitman. p. 122. ISBN 0858962020.
  10. ↑ Hoards of Deep Realm
  11. ↑ MBEE - Microbee (Australian), The Giant List of Classic Game Programmers
  12. ↑ Chilly Willy & Halloween Harry by John Passfield
  13. ↑ Ring of Doom / Ödesringen, Produced by: Microworld, Author: Chris Peters, Year: 1983, System: Microbee, Type: Text adventure ,Tolkien computer games
  14. ↑ Microbee Systems:WHEN OWEN HILL STOOD STILL An interview with Owen Hill, founder of Microbee Systems. Published in Your Computer, February 1986.
  15. ↑ Gamma, Microbee, The As-Yet Unnamed Computer Museum!!
  16. ↑ Microbee Technology Pty Ltd Homepage

External links

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