µPF--2, a µPF--1 clone.

Since a few months, I have been in the process of recreating the well-known µPF--1 microprocessor kit :

Wilipedia.

In fact, this kit has already been recreated, by Wichit Sirichote with the addition of downloading binary files from a PC via a serial interface. 

This solution, more modern than the original kit seems perfect, except that it has some drawbacks and a small operating problem. First, the serial interface comes in the form of a Standard RS232C interface. It would have been really more interesting to offer a serial interface via a USB port. This would have greatly facilitated the use of this kit. On the other hand, the fact that it is the Z80 processor which fully manages the serial interface, the maximum throughput remains very low, at around 1200 Bauds and receives erroneous characters randomly. Downloading even small files takes too long and is unreliable.

Also, I decided to redevelop this kit by offering a much more efficient USB hardware serial interface. I added a serial interface for an external keyboard. The original Wichit Sirichote keyboard being totally unusable. The switches used are not intended for this type of use.

I also added some possibilities and modified the software system accordingly. This allowed me to recreate the kit on a standard FPGA board:

This new system works very well, but on the one hand the FPGA board used is generic and not really suitable for the intended use. This FPGA board also does not offer a USB serial port and the expansion port is not suitable for setting up Z80 type extensions.

So I decided to recreate a system based on an FPGA. After several attempts and configurations considered, I arrived at this system:

Implementing an FPGA is a bit tricky, so I went with a pre-made FPGA board. Going through this type of configuration removes some of the implementation difficulties, and as a bonus, allows me to offer a more 'powerful' FPGA than the circuit originally planned.

The result remains compact and suitable for intensive use. Note also that this system can be used for something completely different than the recreation of the µPF--1 kit since it has 5V compatible serial and parallel inputs / outputs, a 2x16 LCD display in addition to the eight 7-segment displays.

After shipping the design files, I received the printed circuit board. The first thing I did was to see if the FPGA module can be correctly inserted:

Once this check was done I was able to start mounting partially the system. I started by mounting the power parts and checked the absence of 'magic smoke':

Fine! And the USB / serial interface circuit is correctly detected by the system, Win10 in my case.

I was able to continue mounting the board by installing all the components necessary for a first start of the system, i.e. the eight 7-segment displays and the LCD display as well as the interface circuit which will be used to receive the information from the external keyboard:

The FPGA module starts up correctly, The small example which makes the D5 LED flash works. The LEDs and the 7-segment displays are slightly lit which is normal given that all the I / O not used of the FPGA are positioned as inputs with low PULL-UP when it starts up.

It now remains to adapt the code of the FPGA previously developed to this new board.