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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.

Part 1 - MSX Build Power and Reset

The guy who designed this board did up an excellent 68-page document for his board. It goes through theory of operation, design methodology and step by step instructions on how to build the thing. Most instructions for PCBs just say start with the low-profile stuff first and then go up from there. Which is fine but what Alvaro did was introduce a function at a time so will be will following his instructions which includes testing for each function. It starts with the Power and Reset This is the circuit for the power and reset simple. It doesn't use a regulator or have protection, so the power consists of a socket, couple of caps and LED with a resistor

See pretty simple

This is the reset circuit

And this is it in real life

WOW!!

MSX - Artemisa Build

 The MSX computer was an attempt back in the 80's to come up with a standard architecture. It was popular in Japan and Brazil but not so popular in the rest of the world. There are plenty of articles on-line about it's potted history so this is more about the build of a MSX ( the first version ) using the same ICs used back in the day. There are quite a few designs out there but use FGPAs, microcontrollers or other magical items that didn't exist back in the day. Well not as common anyway.

This project can be found on GitHub  and is interesting as it uses the same IC's as an original with a nice layout. Some features like, regulated power supply, parallel port and  +/- 12v power rails would have been nice but would have made the board bigger and more complicated. 

As it worked out the two PCBs required, mainboard and video, came to about $A12.00 for the pair. If there is anyone interested I have 4 I don't need. 

The Blank PCB ready to be filled

And this is the video board.

The PCBs have arrived and just waiting on all the good bits so then get started!