DAI Personal Computer

A DAI personal computer

The DAI personal computer is a rare, early home computer from the Belgian company Data Applications International. The DAI came to market in 1980. It provided many pioneering features such as high resolution color graphics, a maths co-processor, and a pre-compiling BASIC interpreter. But it never became a commercial success.

History

The computer was initially designed by DAI for the UK subsidiary of Texas Instruments for use with the PAL televisions used in Britain^[1]. TI US did not want to build a PAL version of their TI-99/4A home computer, although they subsequently authorized one after they saw the DAI ^[2].

The Dutch educational TV broadcast company Teleac wanted to use the DAI to teach computing, following the BBC's program using the BBC Micro.^{[citation needed]} However, they chose the Exidy Sorcerer instead, because the DAI was not completely ready.

Main technical specifications

The DAI was based on an early 8-bit microprocessor, the Intel 8080 A, (which is generally considered the first really usable microprocessor) and contained on a single printed circuit board all the needed circuitry, some 120 individual ICs. The futuristic-looking white enclosure also held a high quality keyboard, which was uncommon for the time. As a computer display any TV could be used, on which the DAI could display text and high resolution color pictures. It contained a memory controller that enabled it to use up to 48KB of DRAM. This memory was divided in three 16KB regions (memory banks), that could contain either 4K or 16K memory chips. By using memory map switching a total of 72kB of memory was addressable. The DAI also had five programmable interval 64µ - 16ms interval timers that could generate interrupts. The built-in interrupt handler chip could also handle two external interrupt inputs and the interrupts of two serial RS232 UARTS. The DAI featured a DAI/Indata DCE parallel I/O bus for parallel high speed I/O. The DAI also had 3 sound generators and 1 noise generator, and was capable of generating stereo sound.

Graphics capabilities with 48k RAM installed allowed up to 240 x 528 pixels in 4 out of 16 color palette in 4 successive blobs, leaving 16k programming space. The graphics modes were controlled by a device called Programmable Graphics Generator, implementing several techniques:

• decoupling physical scan lines from the 'logical' lines. The repeat count of physical scan lines could be 0 to 15 per line (Due to interlacing a physical scan was two pixels high),
• configurable horizontal resolution per line,
• using indexed colors,
• limit modifying the color palette to one color per line.

In 4 color mode, per logical line one foreground and one background color could be selected, so each line element or logical pixel could be represented by one bit.

In 16 color mode, the color palette was inherited from the previous line. only one of the four usable colors could be changed.

The special thing was, that this limitations were handled by Basic, so the user didn't notice his feet were tied together ^[2] Basic allowed only the whole screen in one mode, but poking directly in memory allowed mixed resolution lines. The whole PGG was implemented with two PROMs and standard TTL logic. The scheme predated the Amiga HAM mode by half a decade.

The BASIC interpreter was remarkably fast for the time because it pre-compiled to an internal byte-code, unlike the Microsoft BASIC interpreter which most other systems of the time used. This is a significantly more difficult trick than doing the same for C or other compiled languages, as the byte-code had to be re-expanded so it could be edited as is usual for BASIC. DAI variables could be up to 14 characters long. The internal byte code used pointers to a variable look up table at the bottom of the code, which made the code extremely compact, despite long variable names.

This technique was rare (only other known example is the ABC 80), and is remarkably similar to that now used for Java.

To enhance the mathematical abilities of BASIC, (and assembler programs) an AMD AM9511 floating point co-processor (compatible with the Intel 8231) could be added.

As a subject for a business management seminar, the development of the DAI PC is fascinating. The first working example was produced in less than 3 months, by 3 people, one of whom was taping up the circuit board layout. All 64K of assembler was the work of one man David Collier, and all the hardware design the work of another David, David Lockey. The original decision to use the 8080A 1 MHz processor(already in use by DAI on other products ) was forced by the ridiculous timescale, which itself was dictated by a desire to show the machine to a TI USA board meeting. In the end only a trip on Concorde got the machine there on time. However the slow CPU dictated a huge amount of work on the pre-compiling BASIC, and the option for hardware-assisted floating point which might not have been required if the newer Z80 had been chosen. If a proper 16-bit CPU could have been applied the machine would have been a real contender, but would certainly have missed the TI and Teleac deadlines. The decision to design the PC to use any old off-the shelf cassette tape recorder made the load and save speeds dauntingly slow. The need to keep the end-user cost down dictated the need for extra complexity to output a TV signal capable of working with a domestic TV, though a dedicated monitor would have been simpler and given better results. Fascinatingly, when TI finally did put the 99/4 onto the European market a few months later, it was initially sold only in a pair with an American NTSC TV because it could not drive European PAL and SECAM ones.

Further technical details

• CPU: an Intel 8080A at 2 MHz
• Memory: a maximum of 48KB dynamic RAM, 24 KB ROM and 256 Bytes of static RAM (stack RAM)
• Keyboard: 56 Keys
• Video interface: a PAL. NTSC or SECAM compatible color-TV output signal
  • Text mode: 60 characters × 24 lines
  • High resolution graphics modes: low - 65 x 88 pixels; medium - 130 x 176 pixels; high - 260 x 352 Pixels
  • available colors: 4 or 16 colors (16 color mode was actually 4 color palette)
• Cassette interface: Audiocassette (600 Baud)
• Alternative main storage systems:
  • The "DAI Memocom Data Recorder" (which used Philips minicassettes)
  • Two eight inch floppy disk drives (which enabled the use of CP/M).
• Peripherals: a card rack, the ("DAI Real World Card System"), could be connected through the DCE-Bus to the DAI.
• Input-Ports: 2 Paddles and two RS-232 serial input ports.
• Output-Ports: 2 stereo audio outputs, and two RS-232 serial output ports.
• Sound generation: 3 stereo voices + 1 noise generator,
• System software:
  • a machine code monitor with the following commands:
    • LOOK
    • DISPLAY
    • GO
    • FILL
    • SUBSTITUTE
    • MOVE
    • EXAMINE
    • EXAMINE REGISTERS
    • VECTOR EXAMINE
    • VECTOR EXAMINE BYTES
    • READ
    • WRITE
  • a built in DAI BASIC interpreter.
• the system was also supported with a 8080-Assembler.
• miscellaneous: a true random number generator implemented in hardware.

References

1. ^ http://www.xs4all.nl/~fjkraan/comp/dai/daipcw.html
2. ^ ^{a b} http://www.xs4all.nl/~fjkraan/comp/dai/insideInfo.html

External links

• extensive info about DAI
• German language site
• the DAI-Computer at old-omputers.com
• many technical details and pictures, in French.