GoWin FPGA & µPF--1

To finalize my uPF--1 compatible board, I decided to implement the Wichit Sirichote's project : 

I have already done this work a few years ago, but based on an Intel FPGA. Since then, I have improved in the VHDL language. 

So I take advantage of this to code the whole machine again in this GoWin FPGA, also taking advantage of the improvements made by the new versions of certain components and the SDCC compiler, as well as the modifications that I have made myself.

This little development machine is very interesting. It allows you to become familiar with the operating principles of microprocessors. 

Modern processors like ARM for example, still work the same way. Understanding how a Z80 works is a very good learning exercise. Much better I think than Arduinos, which, if they have a whole bunch of 'fun' advantages, mask a large part of the real functioning of the processors.

And now with the startup messages:

At the time, I called my work uPF--2. I will continue to name this little machine that way.

This is not a priority project. I will advance it as I can, over time...

uPF--2 : Beginning of electronic board design.

After having worked on several personal electronic boards as well as on the reissue of microcomputers, I can finally start designing my personal FPGA board.

This is a minimal system intended to replace the Z80 µPF--1 compatible development kit that I have mentioned several times on this blog.

The diagram looks something like this:

Overall this board is not very complicated and pretty much picks up the basic elements of the original design. I just added a few useful components that were lacking on the base board. 

I also modified the extension connector to present only a few interesting signals and not all of the data and address buses. I prefer to use expansion boards already created for other systems rather than recreating specific expansions.

It remains now to perform the most difficult part, the routing of the board:

It's not what I like most to achieve ;-)

The uPF--2.

The Wichit Sirichote Z80 MICROPROCESSOR KIT clone : The uPF--2.

I worked on replacing the Wichit kit with an FPGA version. During this work, I said to myself that the keyboard had to be replaced. On one hand because I think that it is impossible to work under good conditions with the original micro-switches, and on the other hand, the multiplexing has not been correctly implemented and can present big problems in the event of simultaneous pressing of several keys. No protection diode and no phantom key suppression as been placed : 

The Wichit Sirichote original design.

Furthermore, I decided to recreate the keyboard as a separate part. This will allow me to develop the processor board independently. However, I also decided not to use a parallel link because it is not practical at all. I preferred to connect the keyboard with a simple serial cable to the processor board.

There are not many solutions for the choice of keys if you want something 'pro'. So I chose the Cherry type keys. For now, I have only studied the keyboard circuit. Here's what it should look like :

To be continued...