Note for Computer Organisation and Architecture - COA by Anil Reddy Maram

Topics ( 4 )

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REGISTER TRANSFER AND MICRO OPERATIONS Register Transfer Language ¾ The symbolic notation used to describe the micro-operation transfers amongst registers is called Register transfer language. ¾ The term "register transfer" means the availability of hardware logic circuits that can perform a stated micro-operation and transfer the result of the operation to the same or another register. ¾ The word “Language “is borrowed from programmer’s, who apply this term to programming languages Register Transfer Information transferred from one register to another is designated in symbolic form by means of replacement operator. R2 ! R1 It denotes the transfer of the data from register R1 into R2. Normally we want the transfer to occur only in predetermined control condition. This can be shown by following if-then statement: if (P=1) then (R2 ! R1) Here P is a control signal generated in the control section. Fig:- Block Diagram of register Control Function A control function is a Boolean variable that is equal to 1 or 0. The control function is shown as: P: R2 ! R1 The control condition is terminated with a colon. It shows that transfer operation can be executed only if P=1. Implementation of controlled transfer P: R2 !R1 MATERIAL PREPARED BY ANIL REDDY [2/4 CSE]

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Block diagram Timing Diagram • The same clock controls the circuits that generate the control function and the destination register • • • • Registers are assumed to use positive-edge-triggered flip-flops If two or more operations are to occur simultaneously, they are separated with commas P: R3 ¬ R5, MAR ¬ IR Here, if the control function P = 1, load the contents of R5 into R3, and at the same time (clock), load the contents of register IR into register MAR Basic Symbols for Register Transfers MATERIAL PREPARED BY ANIL REDDY [2/4 CSE]

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Bus and Memory Transfer Bus Transfer The most efficient way to transfer data is by using a common bus system, which is configured using common bus registers in a multiple register. The structure of the bus consists of a set of lines. These lines are registers of one bit each that transfer only one data at a time. The data transfer is controlled by the control signals. Control signals determine which register is to be selected during each register transfer. To construct a common bus system, two methods are used: 1. Using Multiplexer 2. Using Three States Bus Buffers Multiplexer: The multiplexers select the source register whose binary information is then placed on the bus. The selection lines are connected to the selection inputs of the multiplexers and choose the bits of one register. The construction of a bus system for four registers is shown in Fig: - Bus system for four registers Fig: - Bus system for four registers Each register has four bits, numbered 0 through 3. In order not to complicate the diagram with 16 lines crossing each other, we use labels to show the connections from the outputs of the registers to the inputs of the multiplexers. For example, output 1 of register A is connected to input 0 of MATERIAL PREPARED BY ANIL REDDY [2/4 CSE]