Computer Organization and Architecture

Study Notes

A register transfer language is a system for expressing microoperation sequences among registers in symbolic form.
It is a convenient tool for describing the internal organization of digital computers concisely and precisely.

Computer registers are designated by upper case letters (and optionally followed by digits or letters) to denote the function of the register.
Examples of register designations include MAR (memory address register), PC (program counter), IR (instruction register), and R1 (processor register).
The individual flip-flops in an n-bit register are numbered in sequence from 0 through n-1, starting from 0 in the rightmost position and increasing the numbers toward the left.

A register is commonly represented by a rectangular box with the name of the register inside.
Individual bits can be distinguished, and the numbering of bits in a register can be marked on top of the box.
A 16-bit register can be partitioned into two parts: the low-order byte (bits 0 through 7) and the high-order byte (bits 8 through 15).

Information transfer from one register to another is designated in symbolic form by means of a replacement operator.
The statement R2← R1 denotes a transfer of the content of register R1 into register R2.

A digital system is an interconnection of digital hardware modules, including registers, decoders, arithmetic elements, and control logic.
Digital modules are best defined by the registers they contain and the operations performed on the data stored in them.
A microoperation is an elementary operation performed on the information stored in one or more registers.

Examples of microoperations include shift, count, clear, and load.
The internal hardware organization of a digital computer is best defined by specifying the set of registers, the sequence of microoperations, and the control that initiates them.

RTL is a symbolic notation used to describe the micro-operation transfer among registers.
It provides an organized and concise manner for listing the micro-operation sequences in registers and the control functions that initiate them.
The RTL statement R2← R1 designates a replacement of the content of R2 by the content of R1.
The content of the source register R1 does not change after the transfer.

A control function is a Boolean variable that is equal to 0 or 1.
The control function is included in the statement as P: R2← R1, where P is the control signal generated by a control section.
The control condition is terminated by a colon, implying that the transfer operation is executed by the hardware only if P=1.