Audio Direct Box prototype

I had to wait more than a month this time to receive the printed circuit board of my Audio Direct Box :

There really is a persistent problem with global distribution channels :-(

The problem now is to recover the components necessary for the complete construction of the first 'real' prototype.

To be continued...

Sergey Kiselev MSX OMEGA computer and... a keyboard for it.

 Sergey Kiselev developed some time ago an MSX2 compatible computer :

This is one of the boards that I buid. Building this kind of retro-computer costs a certain price, in particular because of the connectors which are also of the MSX type and are not very affordable today.

In fact, I hesitated to build the keyboard that Sergey developed for this OMEGA, thinking of using a standard and cheaper keyboard either PS / 2 or USB.

Obviously, the most common models today are of the USB type. So I developed a small USB interface on one side and parallel on the other to interface with the keyboard bus of the OMEGA board :

This interface uses a specific processor which manages the USB protocol to which I have added an STM32G0 type processor for the decoding of the USB frames intended for the OMEGA board.

The documentation of the USB management circuit being very ... light, I had some difficulties in retrieving the key code from the USB keyboard.

But here I am:

The right part of the ST IDE displays, among other things, the value of the Key variable, corresponding to the value 0x14. I actually hit the 'A' key on the keyboard, which matches well the 'Q' code on the standard keyboard. And yes, I use a French keyboard ;-)

The code is not very well written yet. All I have to do now is manage the sending protocol to the OMEGA board and I will finally be able to interact with this computer. So far I've only managed to get the init screen, which isn't bad :-)

New retro-computer?

Soon available: a retro computing platform equipped with all the necessary resources for the emulation of existing machines or the development of new concepts.

Its particularities?

16/32 bit compatible. A specific port for processor module. Optionally, 680x0, 486, etc ...

Humor : Finally alone!

 © Synthelectro.

The Wichit Sirichote Z80 MICROPROCESSOR KIT and the µPF--2

After thinking about what could become of my improved version of the Z80 µPF - 1 compatible kit from Wichit Sirichote, I thought that the first thing to do was to take full advantage of the Z80 hardware emulation in the FPGA.

In fact, the Z80 encoded inside the FPGA can operate at the native frequency of the QMTECH board, which is 50MHz. It would be possible I think to go up to 100MHz using a PLL but in the context of a learning board, I did not consider it necessary to exceed 50MHz.

Obviously, it is not enough to change the frequency of the processor to make the system working correctly. Indeed, apart from the internal resources of the FPGA, the external resources operate at much lower frequencies. This is the case off the I2C bus, the LCD display etc etc ...

By properly managing the internal processor frequencie, I have succeeded in achieving a fully functional system. 

So all RAM ROM access and internal FPGA peripherals are now running at 50MHz. This represents a speed approximately 14 times greater than the original 3.579MHz of the Wichit Sirichote Z80 kit. 

This can make it possible to consider applications a little more 'serious' now!

Wichit Sirichote µPF--1@3.579MHz VS µPF--2 @ 50MHz

As can be seen in the image above, the µPF - 2 kit has a separate mechanical keyboard which is very pleasant to use, unlike the keys used on the original kit.

Communication with a PC is now carried out at 38400 baud and no longer 1200 baud. Or a file download speed multiplied by 32!

Obviously, now the file download is proceeding correctly. There is no more corrupted informations. This is mainly due to the fact that I used a real UART and not a slow emulation performed by the Z80, like on the original kit.

The majority of the code now runs at a speed of 50MHz and no longer at around 3.5MHz.

The µPF - 2 kit also offers other resources such as the native LCD display as well as a real-time management circuit.

Z80 @ 50MHz!

To make this all possible, I also rewrote a lot of the code of the monitor. I haven't completely finished this job yet. I also still have a few details to finalize on the VHDL code for the hardware emulation. I expect to carry out these operations in the next few days.

So, I now hear in France, that it is becoming difficult to find people with basic skills in digital electronics and that the National Education no longer trains this type of person.

This is true, and false. False, because a few excellent branches still exist, but very few highly qualified personnel are trained. True because there is no longer any training allowing a larger number of talented people to be trained in this type of technology.

This is nothing new. Reason why I personally learned digital electronics and more particularly processor systems on this type of material, in the 80s.

We may not realize it, but even today, a very large number of applications are built around the Z80 or other processor like the 6502. Modern technology makes it possible to use this processor in an FPGA and thus to obtain inexpensive but nevertheless very powerful hardware. And imagine that it is possible to implement an FPGA with 8 or 16 Z80 cores at 50MHz or 100MHz without problem. What flexibility!

Retro computer : RETRO II, a clone of the APPLE IIe computer.

Among other subjects, I have been assembling for a few weeks an APPLE 2e compatible board, The RETRO II.

I did manage to get the system start page but it wasn't easy. 

More details here: https://sillycony.blogspot.com.

Audio Direct Box prototype.

EasyEda is really an interesting PCB creation tool. I often use it for fairly simple circuits, and it does its job very well. I am currently working on the prototype of one board of my futur multi direct box :

Selection of one of the three unbalanced sources and electrical isolation and symmetrization of the output signal. 

Obviously, it's a little more complicated than performing this function with an audio transformer. And then I would probably have some modifications to make to the schematic based on the measurement results of this prototype...