My friend would like to make an address decoder for Z80 see the truth table:



Blue is "0" and red is "1". How to make the HW logic ?

 

Something with a "look up table" FPGA or perhaps an EPROM.

 

If all bits are 0, return bit 1=1 and bits 2-6 to 0. ELSE, shift bits 4-7 to bits 3-6 and set bit 2 to a 1.

Looks like it could be done with a 74HC30 and a 74HC00 NAND gates.

 

How to make the HW logic ?

Does the solution need to be logic gates? A look up table would be much easier.

 

 

View attachment 306442

And input pin 4 is wired to output pin 3, etc.. to input pin 7 to output pin 6.

Mr Chips solution is much simpler than what I had in mind.