Ultimate MSX cartridge modification

  

I made two final changes to the design of this cartridge. 

First modification.

The first concerns the interfacing circuits with the MSX bus : Aoineko, the developer of the MSXgl graphics library who also tests the cartridge, reported to me problems with random startup of his computer. After studying his problem and especially after looking at the datasheet of his Panasonic FS-A computer, I realized that the power supply of this machine was 'unconventional' to say the least. This results in potential ground problems :

I guess you 'see' what I mean. The wire that serves as a ground reference is one of the two wires of an AC power supply! Hmm, I don't like that at all. 

With this type of design, the ground is always noisy for anyone who wants to connect to this type of device by taking the electrical reference of this ground. 

I therefore powered the cartridge interface circuits no longer directly with +3.3V via the cartridge's internal regulator, but directly via +5V from the MSX computer. No no, the problem was not a bad adaptation of the signal thresholds. TTL circuits work very well with commands not in +5V but in +3.3V. The HIGH level must be at least 2V, which is the case. On the other hand, it is true that this leaves a noise margin of 'only' 1.3V in the case of supplying the interface circuits with 3.3V, and given the design of the Panasonic FS-A1 power supply, I tell myself that that's a bit fair. 

Very good, but then I just postponed the problem elsewhere? It's true. But the interface circuits used, even if they can be powered by 5V, still accept signals coming from circuits powered by 3.3V. The minimum voltage for a high signal is 1.7V on these circuits. I therefore gain 300mV of noise margin. I hope this will be enough.

I still purchased a USB bus isolator in case my modification does not work on the Panasonic FS-A1. This will at least validate my 'theory'.

Second modification.

This time, it is the automatic RESET system of the MSX computer. I implemented directly on the cartridge, a system which allows the computer to be placed in RESET mode for the duration of the cartridge loading. In doing so, and once the cartridge has been loaded correctly, the MSX computer wakes up and boots directly from the cartridge : great!

The small 'problem' of this solution is that it is necessary to intervene inside the MSX computer to locate the reset system, in order to connect the RESET 'wire' coming from the cartridge. 

This is a very simple operation to carry out for those who know how to do it, but this is not the case for everyone. The solution then consists of finding a way to turn off the power to the MSX computer and then turn it back on once the cartridge has been loaded. Without using any wired connection because it is too dangerous. So I opted for a wireless solution.

I bought some small 433MHZ modules:

These models are simple enough to use and small enough to be integrated without major modification on my cartridge.

And there you have it... The first tests were functional. I was able to easily turn on and off a small LED connected to a receiver module placed a few meters away.

The receiver module:

To finalize the subject, all I have to do is develop the receiving system. It will simply appear in the form of a remote controllable mains socket. However, I use universal AC outlets so it can be used just about anywhere :

This circuit is simple and easy to assemble. I also think I will use it not only for the type of application targeted here, but more simply as a remote-controlled socket. You can easily find small remote control 'keys' on the Internet that will work very well with this HF receiver.

Warning :

The HF systems and the design of the cartridge have not been the subject of any certification request. However, the transmission power in games is so low that this does not pose a problem. However, not to be used in a sensitive environment such as healthcare centers....

A MSX flash cartridge downloadable from USB.

 

 

We have to be honest, developing quality equipment is not easy. Downloading a cartridge directly via the USB port from your PC to the MSX computer without any manipulation to do is a good idea.

But we must recognize that it is not done like that! I had to overcome hardware problems, software problems, implementation and component supply problems, etc. etc. 

Fortunately, most difficulties come from not having in-depth knowledge of the issues encountered. This is the study side of 'study and development'. We're getting there but it takes time.

So, after a certain number of prototypes, more and more functional, I am now arriving at the 'final touches'.

What is it about? In fact, with the idea of ​​making the loading and restarting process of the MSX computer automatic, just after copying/pasting a ROM file, you have to... restart the computer.

In 'real' life, a computer requires a power off/on sequence to restart on a new cartridge. This is not very practical. So I had the idea of ​​equipping my cartridge with a RESET signal output for the MSX computer.

Subsequently, it did not pose a problem for me to locate the right place on the OMEGA board to force the reset of the MSX computer.

But... that's not the case for everyone. And truth be told, I don't know many people who want to open up their MSX computer to solder somewhere a 'wire' from the outside.

In fact, you have to 'simulate' the action of the ON/OFF button on the computer. Again, there is no question of 'fiddling' with the computer switch. A relatively simple solution therefore consists of making a remote controllable electrical outlet. Obviously, there can be no question of connecting the MSX cartridge to an electrical outlet in any way.

A possible and elegant solution to this problem is to use an HF link. There is no question here of using a complicated or expensive module but rather a basic 'thing' capable of just remote control something.

After some research, I came across these modules:

I ran some link tests. It works really well. So, and as the emission module is very small, I decided to integrate it into my cartridge. In the end it gives this:

All I have to do now is have a few copies of this new version of the cartridge made. Of course, you will also have to make the 'famous' electrical outlet. I have some ideas for making such a socket 'easily' and very simple to operate, while still being safe to use.

Well, I have the impression of building a castle, but, even if it sometimes happens to have difficulty moving forward in the face of difficulties, it is clear that the subject is progressing and that it works better and better, which provides some satisfaction! 

MSX Omega computer : USB keyboard interface.

A few weeks ago, I talked about Sergey Kiselev's MSX2 compatible processor board project and the choice I made not to build the keyboard for reasons of overall system cost. 

Not everyone will agree with this choice, but for me, the main thing is to be able to have fun in retro-computing without breaking the bank. In fact, I specially studied an adapter for this MSX board to allow the use of a standard USB keyboard:

As usual, after a few days of waiting, I received the PCB:

This board is not particularly easy to assemble by hand because of the two integrated circuits with very thin and close legs. But with a little patience and skill, here we are. First I powered this adapter and plugged in a USB keyboard. I was able to observe the lighting of the keyboard connection LED as well as its flashing each time a key was pressed on the keyboard. It seems to me to be a very good start since the reaction of the USB control IC corresponds to what is indicated in the datasheet. In principle, all that remains is to program the processor to provide the parallel code expected by the MSX board.

A small additional check was carried out to verify that this adapter board fits correctly on the OMEGA board:

Note that I chose a raised USB connector to allow easy insertion of the keyboard connector. My adapter looks perfect! In fact, I have to quickly program it because without a keyboard it is obviously impossible to use the OMEGA computer.

However, for some time I received a Carnivor cartridge to allow me to copy programs or games to it and finally test the proper functioning of the OMEGA board:

At least I have already been able to test that this cartridge fits correctly into the connectors of the OMEGA:

I may also have to find a joystick for this machine. Otherwise it will be difficult for me to really test the games ...

Omega computer : USB keyboard interface.

A few weeks ago, I talked about Sergey Kiselev's MSX2 compatible processor board project. I have completed the assembly of a copy of this board. I like a lot the style of the result:

Personal picture.

I equipped this board with the system, also MSX compatible, C-BIOS ver 0.29. The whole system works perfectly.

Personal picture

But, for the moment, I do not have a keyboard or cartridge to interact with the machine. Given the cost of building this type of material that uses original components, I decided to test the adaptation of a standard USB type keyboard instead.

I have therefore developed a small circuit which will take place in the keyboard connector of the Omega board and will directly provide an input for a USB keyboard:

Personal picture

The finished prototype should look like this:

Personal picture

I must also plan to use a ROM or FLASH cartridge in order to test some software applications. The MSX environment is increasingly dynamic. New games continue to be produced. 2021 looks promising! 

I have some ideas to try to improve the performance of this type of material ...

Retro Computing.

Is retro computing something you just do for fun? Certainly, but not only!

The microcomputers of the 80s were open and easy to program, often in Basic, but also in assembly language. It was quite easy to create cartridges or expansion boards for them. Everyone remembers the Commodores, Atari, Apple, Sinclair, BBC etc etc...

In short, a time of great creative freedom. All this gradually disappeared with the hegemonic position of the PC(IBM) / Microsoft 'association'.

Is it possible to regain some freedom again in this digital world? Yes of course. By resuming and 

continuing the great road of creation abandoned in the early 90s. How? by taking up some good ideas from the time and developing them :

There were a lot of good ideas in the 80s. But, if we take the case of 8-bit machines, the MSX standard was a very good initiative since it allowed a good stadardization of the computers, while preserving a good freedom of design. This standard was originally initiated, among others, by Microsoft : 

To enter the MSX scene, It is obviously possible to equip yourself with some new MSX machines based on an FPGA, but I think that in the introduction, a machine created such as at the time would be a good starting point.

All this written, it remains to find an effective solution to launch into the realization of an MSX machine. Fortunately, Sergey Kiselev has recreated a great MSX computer motherboard called Omega :

My own Omega main board issue.

The Omega computer is not based on any computer that has existed but only on the MSX 2 standard. Therefore, it is necessary to obtain a whole set of obsolete components but still available on the Net.

It may take a little time to build this board but the months ahead should leave time for this task. In the end, it should look like this :

https://www.retrobrewcomputers.org

I am thinking of using my own keyboard version with this Omega.

A good introduction to the MSX standard with the Yamaha CX5M computer, recently published :

Of course there were some great 16/32-bit machines as well, Amiga, 520ST, but that's another story...