Notes on Register Transfer Language

Introduction

• Discussing Register Transfer Language (RTL).
• Understanding the term "register."

What is a Register?

• Definition: A collection of individual flip-flops connected to form registers.
• Notation: Registers are denoted by capital letters (e.g., R1, R2).
• Examples of Registers:
  • Memory Address Register
  • Program Counter
  • Instruction Register
  • Processor Register

Arrangement of Registers

• Example Registers:
  • 8-bit Register: Bits 0 to 7.
  • 16-bit Register: Bits 0 to 15.
• Division of Registers:
  • Higher Order Register (bits 8-15)
  • Lower Order Register (bits 0-7)
  • Example: Program Counter (PC) divided into PC lower and PC higher.

Micro Operations

• Definition: Operations executed on the data stored in registers.
• Relation to Programming:
  • In programming (e.g., C/C++): C = A + B consists of arithmetic (addition) and assignment operations.
  • At the register level, these are termed micro operations, representing basic operations.

Register Transfer Language (RTL)

• Definition: Symbolic notation used to describe micro-operation transfers among registers.
• Function: Represents the transfer of data from one register to another.
• Example Notation:
  • R2 <- R1: Content of R1 transferred to R2.
• Important Operator: The replacement operator (arrow operator) indicating transfer direction (right to left).

Register Transfer Process

• Example: Transferring a 4-bit register R1 containing 1101 to R2.
  • After transfer, R2 will also contain 1101.
• Condition for Transfer:
  • Transfers must occur under predefined conditions (controlled by the control unit).

Control Function

• Definition: A boolean function (value 0 or 1) that determines if a transfer will happen.
• Example:
  • If P = 1, then transfer R1 content to R2.
• Control Signal: Signals control circuit to enable or disable transfer based on the value of P.

Timing and Control Signals

• Clock Operation: R2 operates based on a clock signal.
• Load Signal: Transfer occurs when:
  • Load signal goes high (P = 1), enabling transfer.
  • Transfer occurs when clock signal goes low after P is 1.
• Key Point: Transfer happens on the falling edge of the clock pulse, not when it is high.