Logic Design Conventions

LOGIC DESIGN CONVENTIONS

Types of logic elements

---> Information encoded in binary

• Low voltage = 0, High voltage = 1
• One wire per bit
• Multi-bit data encoded on multi-wire buses

---> Combinational element

• Operate on data
• Output is a function of input
• Output only depends on the current input
• Uses for ALU, multiplier, and other datapath

---> State (sequential) elements

• Store information
• State element to store the states
• Output depends on current inputs and current states 

COMBINATIONAL ELEMENTS

SEQUENTIAL ELEMENTS

Register : stores data in a circuit (use D flip flop)

---> Uses a clock signal to determine when to update the stored value

---> Edge-triggered: update when CLK changes from 0 to 1

The logical operation of the positive edge-triggered D flip-flop is summarized in the table below :

To write new data in the register, we use D flip flop with Write Enable

--->Write Enable:

• 0: Only updates on clock edge where the output of the register becomes the input itself (Data in register will not change.

• 1: New data is fed to the flip-flop and the register changes its state

CLOCKING METHODOLOGY

Clocking methodology

•  Defines when signals can be read and when they can be written
•  Mainstream: An edge triggered methodology
• Determine when data is valid and stable relative to the clock

Typical execution:

– read contents of some state elements,

– send values through some combinational logic

– write results to one or more state elements

BY AINI KHAIRANI BT AZMI