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Building registers and a register bank  				[TOC]
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Starting with a __D flip-flop__ we will build an 8-bit register first and then a
register bank for our ALU.

Description of the register bank:

- It contains 4 registers and each of it can store 8 bits. Each registers has a
  2-bit id (`00`, `01`, `10`, `11`). For simplicity we sometimes call them just
  "register 0", "register 1" which obviously correlates which the interpretation
  of the id as an unsigned integer.
- It supports read and write operations:
    - (_Reading_) With the 2-bit inputs `sel_out0` and `sel_out1` you can select
      from which register you read the content from the 8-bit outputs `out0`
      and `out1` respectively.
    - (_Writing_) With the 2-bit input `sel_in` you can select which register
      gets overwritten with the 8-bit input `in`. Overwriting takes affect if
      the `clock` input is one.

    We will introduce in the next section a more compact notation to address
    a register.

- Special register: Register `reg0` is a _zero register_. It always contains a
  bit pattern with zeros only, i.e. writing to it simply gets ignored, reading
  from it gives always the zeros bit bit pattern.

Video tutorial
==============

In the video I will start with a copy of the final project in session 2.
__This__ is a link to my project for session 2 and if you want you can fork it
so that we start on the same page.

---- VIDEO ------------------------------
https://www.youtube.com/embed/kUDNEQn2TlQ
-----------------------------------------

:links: D flip-flop -> https://en.wikipedia.org/wiki/Flip-flop_(electronics)#D_flip-flop
        This	    -> https://circuitverse.org/users/20564/projects/76282

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