Debugging designs is going to be much easier with a way to see the values being passed around. Using LED's is all well and good but does not scale well to 32 bit buses, especially if you need to look at three such buses at the same time. I would have preferred the debug board be able to show a 32 bit value but it is not possible to fit the 8 segment drivers as well as 8 segment displays on a single board. Instead we will have to settle for half of that.

So time to create a debug board that is able to display the value of a 16 bit input using 7 segment displays as the output. As each 7 segment display needs to shows values from 0 to F that means we need a driver that takes in 4 bits and outputs the appropriate 7 segment output lines. Looking around it is easy to find drivers for decimal (BCD) but they do not show the values from 10 to 15 as the needed hex characters. Instead they all show characters such as h, e, l and p so that you can spell out the word 'help'. The only driver I could find that I could also buy online is the MC14495 from Motorola. They have not been made for quite some time but someone in China has a warehouse full of them because I was able to get 20 of them from AliExpress. Their production dates range from 1987 to 1997.

By applying power but letting the data lines float I get the following example output...

At the top you can see the other board I have created, a simple bus board that has two lanes of 16 bits and will be used to distribute values to various boards in the finished CPU. In this case I am using the first two bits to distribute power and ground to the debug boards.

Yes, these two boards and pretty trivial but when you have never designed any electronics before it is good to start simple and work your way upwards. Small steps!