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!

  

Part 4 - The Testing

 

First Test - Front and Mother Boards

After careful checking and rechecking before and after each component it was time for the 'smoke' test. Connected the two boards together and they went together really well. The put 5 volts to the motherboard. No IC's had been installed yet, just in case there was something really wrong. Putting on the power did nothing 😡 no 5v to any of the IC sockets or 5v to anywhere for that matter. A problem was found on the motherboard, a through hole pad for the 5v didn't go through. It appeared to a problem on the PCB drawing, not the manufacture, but a short link from the 5v in to the connector that feeds the power to the front board sorted it.

When that was fixed all the LEDs on the front that should be on came up nice and brightly. Then following the instructions shorting the ground pins for the other LEDs proved that they worked.

Next will be the next test. Still need to add the ICs yet.

Second Test - Timing/Control, Decoder and Accumulator boards

The testing of these boards is a bit more complex see page 26.

Set up

• Make a temporary connection between SR07 pads on the front panel to MB0-7 pads left of the motherboard.
• Turn on the power. The 'FETCH' LED all the PC and MA registers should be on.
• Because the MB register is wired to the front switches. Flicking the switches will change the MB LEDs, up with light them up.
• The AC register may have some random LED's don't panic, this is normal.
• Set the FAST/SLOW switch to SLOW, up.
• Set the SINGLE/CONT switch to SINGLE, up.
• This will set to slow with single stepping.
• Make an AND instruction by setting all SR switches to 0, down.

Testing the FETCH-EXECUTE cycle

• Press the RUN key.
• RUN LED should light up and the FETCH LED should still be on too.
• FETCH LED will be on for about 12 seconds then go off and then the EXECUTE LED will come on.
• AND LED should be on also.
• After 12 seconds these LEDs should go off and back to FETCH.

During the EXECUTE cycle if there is a number other than 0 in the AC register it would be shifted around 8 bits to the right.

Testing the indirect addressing

• Set SR4 to 1 to emulate indirect addressing.
• Press the RUN key.
• This should make it run as before but the DEFER LED will be on for 12 seconds before the EXECUTE LED

Testing the TAD instruction

With everything set up as above set SR5 to up to simulate a TAD instruction.

Press the RUN key and should be the same as AND but this time TAD.

All other primary instructions can be checked the same way by using SR5,6,7 and observing the centre cluster of LEDs

Full Parts list and suppliers

 This is a full list of bits for the EDUC-8

All the parts

Value	Component Description	Qty	Supplier	Part #	E8/F	E8/C	E8/T	E8/D	E8/A	E8/P	E8/M	E8/IOT
0.047uF	Cap Greencap	25	Altronics	R2728A			4	3	4	5	5	4
0.1uF	Cap Greencap	9	Altronics	R2865	6	3
0.001uF	Cap Greencap	1	Altronics	R2700B	1
220pF	Cap Ceramic	1	Altronics	R2826			1
100pF	Cap Ceramic	1	Altronics	R2822	1
47uF	Cap Tantalum	2	Altronics	R4805	1		1
100k	Res 1/4 W Resisitors	1	Altronics	R7606			1
10k	Res 1/4 W Resisitors	19	Altronics	R7582	18		1
180ohm	Res 1/4 W Resisitors	42	Altronics	R7540	42
1k	Res 1/4 W Resisitors	5	Altronics	R7558	1							4
2.2k	Res 1/4 W Resisitors	9	Altronics	R7566			2	2	3	2
22k	Res 1/4 W Resisitors	1	Altronics	R7590	1
470ohm	Res 1/4 W Resisitors	3	Altronics	R7550		2	1
680ohm	Res 1/4 W Resisitors	2	Altronics	R7554		2
820ohm	Res 1/4 W Resisitors	1	Altronics	R7602					1
BC548	Transistor or BC108, BC208, BC548 NPN	1	Altronics	Z1042			1
7400	IC Quad 2 Input NAND Gate	37	Unicorn	7400	4		9	8	2	5	6	3
7480	IC Gated Full Adder	1	Unicorn	7480						1
7401	IC Quad 2 Input NAND Gate (OC)	6	Unicorn	7401					2	1	1	2
7405	IC Hex Inverter (Open Collector)	9	Unicorn	7405	5				2		2
7410	IC Triple 3 Input NAND Gate	7	Unicorn	7410			2	2	1	2
7413	IC Dual Input Schmitt Trigger	1	Unicorn	7413			1
7417	IC Hex Buffer/Driver (O.C. - High Voltage)	2	Unicorn	7417	2
7437	IC Quad 2 input buffer	3	Unicorn	7437								3
7496	IC 5 Bit Shift Register	4	Unicorn	7496						2	2
74154	IC 4 to 16 Line Decoder/Demultiplexer	1	Unicorn	74154			1
74161	IC Synchronous 4 Bit Binary Counter	1	Unicorn	74161			1
2125	IC "1,024 x 1 Static RAM (450 ns)"	2	Unicorn	2102							2
7404	IC Hex Inverter	13	Unicorn	7404			4	2	1	2	1	3
7420	IC Dual 4 Input NAND Gate	2	Unicorn	7420			1	1
7473	IC Dual JK Flip Flop with Clear	2	Unicorn	7473			2
7493	IC 4-Bit counter	1	Unicorn	7493							1
7495	IC 4 Bit Right Shift/Left Shift Register	4	Unicorn	7495					2		2
9602	IC Dual Monostable Multivibrator	1	Unicorn	9602	1
74259	IC Eight bit addressable latch	1	Unicorn	74259				1
74105	IC High speed J-K flip-flop (9001 eqv)	1	Unicorn	74105						1
74157	IC Quad 2-input multiplexer (9322 eqv)	1	Unicorn	74157							1
14 Pin	Socket 14 pin DIP	96	Altronics	P0532	11	0	19	13	10	14	18	11
16 Pin	Socket 16 pin DIP	3	Altronics	P0534	1		1	1
24 Pin	Socket 24 pin DIP	1	Altronics	P0540			1
6 pin	Socket 6-Pin Din socket	3	Jaycar	PS0354	3
72 pin	Socket JAMMA Connector	3	Aliexpress			3
36 Pin	Socket JAMMA Connector	7	Aliexpress			7
7101	Switch Red Paddle Type (Data)	8	Aliexpress	R801	8
7101	Switch Grey Paddle	2	Aliexpress		2
7108	Switch Red Spring Return	3	Aliexpress		3
7108	Switch Black Paddle	2	Aliexpress	7101	2
LED	Diode LED 5mm	42	Altronics	Z080	42
E8/F	PCB Front PCB	1	JLCPCB		1
E/C	PCB Motherboard	1	JLCPCB			1
E8/T	PCB Timing	1	JLCPCB				1
E8/D	PCB Decoder	1	JLCPCB					1
E8/A	PCB Accumlator	1	JLCPCB						1
E8/M	PCB Memory	1	JLCPCB							1
E8/P	PCB Programm Counter	1	JLCPCB								1
E8/IOT	PCB IOT	1	JLCPCB									1

Note:
The JAMMA Connectors used here are right for Gwlynns PCB's but if you are using the original PCBs they will need to be cut short.
AliExpress didn't have grey paddle switches so had to print my own greys. You can either put up with using Red or go to Thingiverse (or this one ) and print your own. Suggest using a resin printer for this as it will come out better.
The PCBs can be made by any mob. JLCPCB have a minimum order of 5 PCBs but were pretty cheap and did an excellent job but freight. Which wasn't cheap. :(