Here's an article about the Z80 internals that some may find interesting.
Ken Shirriff's blog: The Z-80 has a 4-bit ALU. Here's how it works. (http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html)
He's at it again. And this time it's our beloved Z80. :)
The first blog entry concerning the Z80:
Ken Shirriff's blog: Reverse-engineering the Z-80: the silicon for two (http://www.righto.com/2013/09/understanding-z-80-processor-one-gate.html)