In 8085 Microprocessor how register transfer is made ?

Information transfer from one register to another is designated in symbolic form by mean of a replacement  operator . The statement

                                               

                                                   R2 <- R1

denotes a transfaer of content of register R1 into R2 . It designates a replacement of the content of R2 by the content of R1 . By definition, the content of the source register R1 does not change after the transfer .

A statement that specify the register transfer implies that circuit are available form the output of the source register to to the inputs of the destination register and that the destination register has a parallel load capacity . Normally, we want the transfer occur only under a predetermined controll condition. This can be shown by means of an if-then statement. 

                                                        

                                                    if(p=1) then (R2 <- R1)

where P is the control signal generated in the control section. It is something convenient to separate the control variable from the register transfer operation by specifying a control function. A control function is a Boolean variable that is equal to 0 or 1. The control function included the statement as follows :

                                                    P : R2 <- R1

The control condition is terminated with a colon. Its symbolized the requirement. That the transfer operation be executed by the hardware only if P = 1.

Every statement written in a register transfer notation implies a hardware construction for implementing the transfer. fig-1 shows the blog diagram that indicates the transfer from R1 to R2 . Then n output of the register R1 are connected to the n input of register R2. the letter n 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 control variable p. It is assumed that the control variable is synchronize with the same clock as the one applied to the register. As shown in the timing diagram.

Fig-1 Transfer from R1 to R2 when p=1.

                                                         timing diagram