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....

8 Ports USB Midi interface.

 

This topic is a very long-standing one for me. I must have started thinking about it in the early 90s. At the time, the power of microcontrollers did not allow the development of complex systems. I then remember having developed a 68000 system to manage the 8 MIDI ports. I never created this system because I realized that it was far too complex to create and therefore necessarily too expensive.

10 years later, at the beginning of the 2000s, things improved in terms of the possibilities of embedded systems. So I tried to create this multi MIDI port using a micro-controller. I almost got there, but ran into a small problem, it was still difficult to find a circuit offering 8 serial ports and fast enough to manage them.

Everything changed in the early 2010s. At that time, it became possible to find a micro-controller circuit with 8 serial ports and enough power to manage everything. It was then that I looked into ARM type circuits from STmicro. From that point on, the problem shifted from the hardware to myself. In fact, in view of the possibilities of the new circuits, I wanted to add a whole bunch of functionalities, including USB bus management. Then, I entered into a spiral of redefining the functions of the object which, constantly, made me experiment with various solutions, all nevertheless unsatisfactory in my eyes. Unsatisfactory, because of the poorly defined hardware, and/or the software functionalities, which are also poorly chosen.

But, this series of failures allowed me to test a lot of solutions. And, a few days ago, as I was rearranging my stack of synths and rewiring everything, the obvious solution dawned on me. Now, right away, I saw very clearly what system I needed to have on hand to allow me to easily and flexibly wire all of my machines. I also realized that I wasn't far from the real subject, in fact. And that I just had to use all my previous developments and my previous ideas to achieve what I needed.

First, create not a hub or a switch, but simply an 8-port MIDI interface. I already have the prototype almost available. I just need to make some minor modifications to allow my 8 ports prototype to be connected to the USB port. So I have just made the necessary modifications to the circuit. 

The general idea is that it should remain simple to achieve. Thanks to the experience acquired with RISC-V processors during my previous work, I left with this type of processor :

It's a fact, the printed circuit board does not seem very complicated to make. Once the components are implemented, it should look like this:

As you might expect, the MIDI connectors are not shown in this 3D view. In fact, it is not standard MIDI connectors but RJ45 connectors that are used. This is a particular characteristic of my system.

 

The difficulty for me is not the creation of the card but its programming. Working with the USB bus is not always easy. Fortunately, a few years ago I implemented a 2-port MIDI interface on a USB port using an ARM microcontroller from STmicro. So I have a software base, I'm not starting from scratch. Even if this does not guarantee that I will reach the end, I also have no means of debugging the USB bus, I am relying on the experience acquired to complete this subject.

 

A MSX flash cartridge downloadable from USB : the last iteration.

 

 What is it about this time?

• I did some redrawing work on certain tracks to make them more 'homogeneous'.
  
  
• I powered certain interface circuits directly via the +5V power supply from the MSX connector and no longer with the 3.3V coming from the 5V USB to 3.3V régulator. the goal being to avoid electrical level problems with the test machine, a Panasonic FS-A1. In theory, 3.3V interfacing should not pose any problems, but in reality, it does.
  
  
• And, I also added a small HF remote control module. This involves controlling remotely and without a physical link, an electrical outlet to automatically restart the MSX computer without having to manipulate the main switch, nor having to 'fiddle' with a RESET connection inside the computer. MSX. 

The final circuit should look like this :

Apart from the location of the HF module, the circuit looks almost the same as the previous version. Having written this, I also adjusted the external dimensions of the card so that insertion into the MSX connector no longer presents any potential gaps.

The final appearance should look very similar to this:

As for the code, the two programs concerning the processor which takes care of the USB communication and the one which manages the MSX bus, should not be modified. From the tests done, loading and making the loaded ROM available for the MSX computer works fine now.

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!