Excalibur 64

 Back in the day, early 80's, there were many Australian companies vying for a piece of the emerging home computer market. Microbee is probably the most prolific. It managed to get their computers into many schools. But there are many that experienced varying degrees of success. The Excalibur 64 was not one of them. Full story below but it had a short history but not many were made. 

In the tradition of dragging late 20th century computers into the 21st this project hopes to recreate one using a mixture of old and new parts. Idea is to use modern components when it doesn't effect the function or IO. For example instead of using two 2764 EPROM just use one monster 1Mb 39SF010 flash IC. But then using the original 8253 timer IC for the audio and the MC6845 for the video.

No substituting with microcontrollers or FPGAs all the obsolete parts are available as new old stock so no excuses. But might use a RPi Pico for video or EPROM emulation for development but not for the final product.

If I could ever get hold of a PCB layout I would like to make an exact replica until then it will be just redoing the pdf version into Kicad and hope the orginals are accurate and I don't make too many mistakes. Already on version 3 of the PCB

Info at a glance

Name  Excalibur 64
Manufacturer  BGR Computers P/L
Introduced 1st July 1983 
Discontinued  31st August 1984
Cost  $399

Processor  Zilog Z80 CPU Clock  4Mhz

Microsoft BASIC built in, CP/M compatible
Memory 

DRAM 64k

ROM   16k

Screen RAM 2K SRAM (separate from user RAM)

Connection 

2 expansion connectors

Cassette I/O

Video RF Output and RGB

RS232C

Centronics Parallel Port

2 Floppy drive connectors via expansion card

Video

16 foreground and 8 background colours

Display: 24 lines by 40 characters and 24 lines by 80 characters, 7 x 12 dot matrix.

Resolution: Low res 320 x 288, 

Graphics Mode: 128 programmable characters, 96 ASCII characters and 128 graphic characters.

Peripherals

A range of peripherals, or add-ons' were developed for the machine by Mick Gulovsen and these included 

1. A RAM upgrade from 64k to 512k
2. 1200/75 baud internal modem used to connect to [[FidoNet]]
3. Keyboard buffer that could buffer up to 16 characters
4.  HIRES graphic add-on board increased the resolution to 640 x 288 pixels
5. Other peripherals had been developed by various users. 

Complete Systems

Later versions were sold as a complete system and included:

1. Dual 5 ¼ inch floppy disk drives 
2. CP/M 2.2 Operating system and later CP/M/ZCPR 3.0 and 3.1 
3. Programming languages Forth, Pascal, and Fortran on ROM and Tape
4. Increased CPU speed from 3.5Mhz to 4Mhz
5. Joystick controller
6. Voice synthesiser

History

The Excalibur 64 was a kit computer released by the now defunct Australian company BGR Computers. The Excalibur 64 sold from July 1983 to August 1984.

BGR Computers was established January 1983 with the intent of developing a system similar to the MicroBee to a foot hold in both the educational and business markets. The company at time wanted to develop a complete system but the costs of development and availability of software made this prohibitive.  Therefore, to enter the fledging home computer market BGR engaged an independent design company to develop a diskless kit which was first advertised in the July's 1983 edition of Electronics Australia .

More that 300 kits were sold and with the help of user groups the software catalogue grew and included, games, utilities and educational programs. 

By December 1983 the Excalibur 64 was released as a complete system the retail price jumped from $399 to $699 but was fully built and tested. This price did not include a monitor and a disc controller board that could run up to four 5 ¼ or 8-inch drives would cost a further $299. 

Reception

It is believed that just over 1000 units were sold. User groups were established across the country and were active 

Useful Links

Dontronics Excalibur

Some Images

Floppy Drive controller 5.25" and 8"

New Freebee Frames

 New Freebee keyboard frames arrived Friday!! 11 - April

They are 1.6mm the Cherry MX spec says 1mm for a frame but these still click in nicely

They didn't go on the first build as I didn't have them and too keen to get is going.

Got 5 from JLCPB they are actually black. Dodgy lighting :/

Smaller images for the MSPP Forum

Images for forums

 Random Snap shots for forums

Freebe Fremium Build

My first (working) Microbee

Being a Z80 I wasn't overly keen on the Microbee so for many years didn't really bother with it. 6502 was the only decent CPU 😝. But the Microbee was the computer we used at school, 16 in a Starnet config. Programming games such as "Lemonade Stand" and of the venerable "Guessing Game". 

Anyway this is a, sort of, build log for the Freebee Premium. A MicroBee imagining designed by Suzy Jackson. See her blog for all the gory details but in short the specs are:

• 32K of general purpose RAM
• 32K of Video RAM
• 64K of EPROM, enough to boot into Microbee 5.22e basic without a core board
• Can run at either 6.75 or 13.5 MHz
• Has all the good I/O, parallel, serial and Tape
• Option to plug in core boards

All open source!!

Getting the bits

Suzy provides a BOM with the part number and suppliers. I used most of this but some items I found either cheaper or from places I prefer not to use, like e-bay. All the 74 logic ICs and passives that I needed to order were from either Mouser or Digikey. It's great that Suzy included the part numbers as sometimes a description can be somewhat ambiguous. Some different sources where;

• Unicorn Electronics for the SY6545, Z84C20 and Z84C00.
• Utsource for the HM62256ALSP and the SN76489A
• Power switch and speaker from Farnell

The Unicorn website looks like it's from the early 90's their freight to Australia is slow and expensive but have some good old new stock just best to buy a few things if buying from them. 

Never used Utsource before this build. Always nervous of suppliers I find just by scouring the internet but they were actually very good. Freight was ok price and quick so will be using them again for hard-to-find parts.

Have used Farnell for years and may not always be the cheapest but are fast and reliable. In this case they were cheaper for the speaker and switch!

The actual build

Suzy provides a construction manual which is great. All components are through hole and all on a single PCB so all pretty straight forward. 

Was so keen to get started I neglected to take a photo before the build but it was this but without all the components stuck to it. This was how it was left for couple of weeks while waiting for the Unicorn order and other bits I neglected to order the first time round. Assumed I already had them 😖

Just testing a core board fits. Shouldn't have doubted but wanted to play while waiting for bits.

Complete! Well almost missing a few buttons but not putting in 64 Cherry MX keys in until I know it works. 

 

Well if does work. There was a bit of phaffing about with the ROM. Evedently you need the BASIC firmwire to get it to work. Suzy has fixed it now so if it's not there it will still boot.

Some More pics top and bottom. Just a few mods but nothing too hard.

And this is Fusion 360 case currently in the works. Still needs some work. And a keyboard cover!!

 

        MREQ and WR

MREQ and RD

Clock and Dot

Thumbs

Boards a here - FreeBee

 The boards finally came via a slow boat from China. Need to finish of the MSX then straight onto this.

Suzy's Microbee Freebee Build

 After reading Suzy's blog on redesigning the Microbee computer from the early 80's I needed to have my own. Her design uses mostly modern ICs but still in keeping with the spirit of the original design. As in no CLPDs or FPGAs or any other forms of magic. 

Part 2 - MSX Build Clock Circuit

Next stage is a little more interesting, the clock generation circuit is installed. The computer uses on crystal at 3.58Mhz to clock the CPU and then uses a flip-flop to divide the clock by 2 and that is used for the Programmable Sound Generator (PSG)

The clock circuit

And in real life 

Look we have a glowing LED!! Checked the frequency output with a CRO and good on both outputs. Next is the big stuff, CPU and the System Bus control ICs.