Introduction to Registers

Objectives

1. Begin to investigate basic "stock" components

Notes

• This is from Carpinelli chapter 4.
• And I will supplement this with other material.
• We have learned how to design our own basic circuits.
• But there are a number of pre-designed components that are very useful.
• The Decoder is one of these.
• But a side trip into registers.
  • I want the register as an example for now.
  • Later we will be back to discuss registers in detail.
• Registers are the place we store data when performing calculations in the CPU
  • They are stock components.
  • A CPU normally has between 1 and 32 of them for general purpose use.
  • A CPU has a number of special purpose registers as well.
• Registers hold a n bits of data.
• Registers are an example of sequential circuits.
• The Simplest Registers Have
  • an n bit data in line, D
  • an n bit data out line, Q
  • A clock line, C
  • A an enable line, EN, sometimes EN
  • 
• A register will store the data on D in the register when the clock changes from low to high.
• To do so
  • Place the data on the d line
  • Hold this for the setup time
  • Enable the register (might be a 0)
  • Change the clock from low to high
  • Hold data for a the hold time
  • There might be an additional time for the register to "stabilize" and the output data to become usable.
• There are registers in Digital
• There are also a number of registers on a chip, the 74377 is one.
• data sheet.
• Timing for the 74377
  • 
  • 
  • 
• Again, we will build registers later.
• Digital File.
• In a modern computer, we will probably have multiple registers.
  • The instruction will contain the register we wish to select.
  • load r3, 3421 says to load 3421 into register 3.
  • The value 3 is hard coded into this instruction.
• So we will need a mechanism to select register 3.