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— Private: Computer —


When I worked through a microcomputer course by HP in 1979, a light went up: You can do everything with a computer, just think and program, all at no cost. Just one initial financial investment. This was an ignis fatuus — a friar's lantern as it turned out soon enough. In 1980 I purchased the Sinclair ZX80 with a Z80 processor clocked at 3.25 MHz, the 4 KB ROM comprised the operating system and a BASIC interpreter. There was 1 KB to store the data and that all cost as much as an office computer with a Pentium V and a 150 GB hard disk in 2007. Soon, a 16 KB RAM pack was added and the money laid out for it would buy a 4 GB USB stick in 2007. The 16 KB data could be saved on an audio cassette, which took 7 minutes.

I soon hit the limit. The ZX81 ROM was purchased (all had to be imported from the UK in those times) and a usable keyboard was built. Together with a friend we built the hardware anew — on a bread board which could accept 14 x 10 16 pin IC's. Almost 100 simple logical circuits were connected up using wire wrapping. We wanted to understand what really was going on and got 64 KB of RAM, besides. An electric daisywheel typewriter was modified and an interface built for it. This printer made 7 impacts per second and the quality of the print was fantastic, so was the wear of the daisywheels. The ZX81 ROM was disassembled part by part and printed. Finally, hard- and software were fully understood. There was no unknown bit at any time.


Once the content of the ROM was known, I programmed additional functions in machine language, extended the existing BASIC with EPROM's, more fonts and routines for further hardware were added. Later, a FORTH-ROM was ordered. A toggle switch permitted to boot either Sinclair BASIC or Husband FORTH — this was a bit like a Windows - Linux multiboot system today.

CP/M (Control Program for Microcomputers)

Then, I purchased an Osborne Executive computer with a 7 inch monochrome amber display — a portable computer with a handlebar. Very modern with the CP/M+ (CP/M 3) operating system, a Z80 processor clocked at 4 MHz, 128 KB of RAM in 2 memory banks, 2 5¼" disk drives (single sided, 183 KB capacity). The ultimate superfast gamer machine is lower priced at 2007 than the Osborne was then. However, a Microsoft BASIC, a SuperCalc spreadsheet, WordStar, a Perl database system, a compiler BASIC and an alternate UCSD-p operation system were all included.



The modified Sinclair ZX80/81 was retired and a new computer was built. Instead of the huge «motherboard» a Z80 bus was introduced. The CPU with RAM and ROM was wrapped on a board that could be plugged into the frame at any place. Additional cards were 'IC-ised'. An EPROM burner was built in order to be able to upgrade the firmware. I developped my own parallel interface, the hardware based on a simplified IEEE-488 (IEC-625) standard, as for the handshaking protocol, I invented my own. This enabled me to connect the Osborne to the new computer. The interface handled a throughput of 20 KB over 20 m (60 ft) reliably.

SBCS Board

A plug-in card with a phoneme synthesizer was developed as well. On the Osborne, I wrote software in compiler BASIC that could prepare texts written in English, German or French and send them to the phoneme synthesizer, which in turn spoke the texts to me.


Then, the PC-DOS machines came. Also this operating system was easy to comprehend, after all, it was — in long parts — just a copy of CP/M. The plug-in card computer got obsolete. The next project was a CPAC which was featured in the German computer magazine c't. I built 7 units. It is a highly integrated system based on the Z80 (I had acquired a fairly profound grip on the hardware in the meantime) with 32 KB EPROM and 32 KB RAM, a serial and parallel interface, extendable Z80 bus, and so on. I wrote my own operating system for it. Without keyboard and display, the units have to be controlled by a «real» computer via the RS-232C interface.

Two CPAC's are in service, one as a test unit (yes, it does work over the Ethernet with an appropriate RS-232C to LAN converter), the other one controls a self built two channel analogue-digital-analogue converter. Put in front of a cathode-ray oscilloscope it makes a storage oscilloscope and used together with a HP wave analyzer this makes an audio frequency spectrum analyzer. This ADA converter can be used as a data logger, too.

There are links to more elaborate presentations of my hardware projects under the Projects heading.

  © 2004 - 2017 by Horo Wernli.