Register Transfer I Leo Tutorial I

Register Transfer Micro-operation : Computer resisters are designated by capital letters ( sometimes followed by numeral ) to denote the function of the register. For example, the register that holds an address register and is designated by the name MAR . Other designations for register are PC ( for program counter ), IR ( for instruction register ), and R1 ( for 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. The most simple way to represent register is by a rectangular box with register name written inside the box, PC (L) refer to the low - order byte and PC (H) to the high order byte.
                 By using replacement operator information is transferred from one register to another.
                                                       R2<R1
                 denotes that content of R1 is transferred to R2.



                                                     Normally, the transfer occurs only under a predetermined control condition. This can be shown by means of an if-then statement.

Every statement written in a register transfer notation implies a hardware construction for implementing the transfer that depicts the transfer from R1 to R2. The n-outputs of register R1 are connected to the n inputs of register R2. the letter n will be used to indicate any number of bits for the register. It will be replaced by an actual number when the length of the register is known. Register R2 has a load input that is activated by the control variable P. It is assumed that the control variable is synchronized with the same clock as the one applied to the reister. As shown in the timing diagram P is activated in the control section by the rising edge of a clock pulse at time t. The next positive transition of the clock at time t + 1 finds the loads input and the data inputs of R2 are then loaded into the register in parallel. P may go back to 0 at time t + 1 ; otherwise the transfer will occur with every clock pulse transition while P remains active.
The clock is not included as a variable in the register transfer statements.
                   The basic symbols of the register transfer notation are listed .Registers are denoted by Capital letters , and numerals may follow the letters . Parentheses are use to denote a part of a register by specifying the range of bits or by giving a symbol name to a portion of a register .The arrow denotes a transfer of information and the direction of transfer. A comma is used to separate two or more operations that are executed at the same time.

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