REGISTER TRANSFER AND MICROOPERATIONS

Transcription

1 REGISTER TRANSFER AND MICROOPERATIONS Register Transfer Language Register Transfer Bus and Memory Transfers Arithmetic Microoperations Logic Microoperations Shift Microoperations Arithmetic Logic Shift Unit Computer Organization

2 2 MICROOPERATION Register Transfer Language An elementary operation performed during one clock pulse, on the information stored in one or more registers Registers (R) ALU (f) clock cycle R f(r, R) f: shift, count, clear, load, add,... Computer Organization

3 3 Register Transfer Language REGISTER TRANSFER LANGUAGE Definition of the (internal) organization of a computer - Set of registers and their functions - Microoperations Set Set of allowable microoperations provided by the organization of the computer - Control signals that initiate the sequence of microoperations For any function of the computer, a sequence of microoperations is used to describe it ----> Register transfer language - A symbolic language - A convenient tool for describing the internal organization of digital computers - Can also be used to facilitate the design process of digital systems.

4 4 REGISTER TRANSFER Register Transfer Designation of a register - a register - portion of a register - a bit of a register Common ways of drawing the block diagram of a register Register R Showing individual bits R2 Numbering of bits PC(H) PC(L) Subfields Representation of a transfer(parallel) R2 R A simultaneous transfer of all bits from the source to the destination register, during one clock pulse Representation of a controlled(conditional) transfer P: R2 R A binary condition(p=) which determines when the transfer is to occur If (p=) then (R2 R)

5 5 Register Transfer HARDWARE IMPLEMENTATION OF CONTROLLED TRANSFERS Implementation of controlled transfer P: R2 R Block diagram Control Circuit P Load R2 R n Clock Timing diagram t t+ Clock Load Transfer occurs here Basic Symbols for Register Transfers Symbols Description Meaning Capital letters Denotes a register MAR, R2 and numerals Parentheses ( ) Denotes a part of a register R2(-7), R2(L) Arrow Denotes transfer of information R2 R Colon : Denotes termination of control function P: Comma, Separates two micro-operations A B, B A

6 6 BUS AND MEMORY TRANSFER Bus is a path(of a group of wires) over which information is transferred, from any of several sources to any of several destinations. From a register to bus: BUS <- R Bus and Memory Transfers Register A Register B Register C Register D Bus lines Register A Register B Register C Register D B C D B C D B C D B C D x 4 x 4 x 4 x x select y 4-line bus

7 7 Bus and Memory Transfers TRANSFER FROM BUS TO A DESTINATION REGISTER Bus lines Reg. R Reg. R Reg. R2 Reg. R3 Load Select z w D D D 2 D 3 2 x 4 Decoder E (enable) Three-State Bus Buffers Normal input A Control input C Output Y=A if C= High-impedence if C= Bus line with three-state buffers Select Enable S S A B C D 2 3 Bus line for bit

8 8 MEMORY TRANSFERS Bus and Memory Transfers AR Memory unit Read Write DR Memory read micro-op: DR M ( DR M[AR] ) Memory write micro-op: M DR ( M[AR] DR ) A B Summary of Register Transfer Microoperations Transfer content of reg. B into reg. A AR DR(AD) Transfer content of AD portion of reg. DR into reg. AR A constant Transfer a binary constant into reg. A ABUS R, Transfer content of R into bus A and, at the same time, R2 ABUS transfer content of bus A into R2 AR Address register DR Data register M[R] Memory word specified by reg. R M Equivalent to M[AR] DR M Memory read operation: transfers content of memory word specified by AR into DR M DR Memory write operation: transfers content of DR into memory word specified by AR

9 9 Arithmetic Microoperations ARITHMETIC MICROOPERATIONS Four types of microoperations - Register transfer microoperations - Arithmetic microoperations - Logic microoperations - Shift microoperations * Summary of Arithmetic Micro-Operations R3 R + R2 Contents of R plus R2 transferred to R3 R3 R - R2 Contents of R minus R2 transferred to R3 R2 R2 Complement the contents of R2 R2 R2 + 2's complement the contents of R2 (negate) R3 R + R2 + subtraction R R + Increment R R - Decrement

10 BINARY ADDER Arithmetic Microoperations Binary Adder B3 A3 C3 B2 A2 C2 B A C B A C C4 S3 S2 S S Binary Adder-Subtractor B3 A3 B2 A2 B A B A M C3 C2 C C C4 Binary Incrementer S3 A3 S2 A2 S A S A x HA y x HA y x HA y x HA y C S C S C S C S C4 S3 S2 S S

11 ARITHMETIC CIRCUIT Arithmetic Microoperations Cin S S A B A B A2 B2 A3 B3 S S 2 3 S S 2 3 S S 2 3 4x 4x 4x S S 4x 2 3 X Y X Y X2 Y2 X3 Y3 C C C C2 C2 C3 C3 C4 D D D2 D3 Cout Computer Organization S S Cin Y Output Microoperation B D = A + B Add B D = A + B + Add with carry B D = A + B Subtract with borrow B D = A + B + Subtract D = A Transfer A D = A + Increment A D = A - Decrement A D = A Transfer A

12 2 LOGIC MICROOPERATIONS Logic Microoperations Specify binary operations on the strings of bits in registers. - useful for bit manipulations on binary data AND: Mask out certain group of bits OR : Merge binary or character data - useful for making logical decisions based on the bit value Applications Manipulating individual bits or a field(portion) of a word in a register - Selective-set A + B - Selective-complement A B - Selective-clear A B - Mask (Delete) A B - Insert (A B) + C - Compare A B - Packing (A B) + C - Unpacking A B

13 3 LIST OF LOGIC MICROOPERATIONS List of Logic Micro-Operations - 6 different logic operations with 2 binary vars. - n binary vars -> functions 2 2 n Truth tables for 6 functions of 2 variables and the corresponding 6 logic micro-operations x y Boolean Function Micro- Operations Name F = F <- Clear F = xy F <- A B AND F2 = xy' F <- A B F3 = x F <- A Transfer A F4 = x'y F <- A B F5 = y F <- B Transfer B F6 = x y F <- A B Exclusive-OR F7 = x + y F <- A B OR F8 = (x + y)' F <- (A B) NOR F9 = (x y)' F <- (A B) Exclusive-NOR F = y' F <- B Complement B F = x + y' F <- A B F2 = x' F <- A Complement A F3 = x' + y F <- A B F4 = (xy)' F <- (A B) NAND F5 = F <- all 's Set to all 's Logic Microoperations

14 4 Logic Microoperations HARDWARE IMPLEMENTATION OF LOGIC MICROOPERATIONS A i B i 2 4 X F i S S 3 Select Function table S S Output µ-operation F = A B AND F = A B OR F = A B XOR F = A Complement

15 5 SHIFT MICROOPERATIONS Shift Microoperations Shifts - Logical shift : shift in a into the extreme flip-flop - Circular shift : circulates the bits of the register around the two ends - Arithmetic shift : shifts a signed number (shift with sign extension) Left shift -> multiplied by 2 Right shift -> divided by 2 Arithmetic shifts for signed binary numbers - Arithmetic shift-right Sign bit R n- R n-2 R R - Arithmetic shift-left Overflow V = R n- R n-2 Shift Micro-Operations Symbol Description R shl R Shift-left register R R shr R Shift-right register R R cil R Circular shift-left register R R cir R Circular right-shift register R R ashl R R ashr R Arithmetic shift-left register R Arithmetic shift-right register R

16 6 Shift Microoperations HARDWARE IMPLEMENTATION OF SHIFT MICROOPERATIONS Serial input (I R ) Select for shift right (down) for shift left (up) S H A A A2 S H A3 S H2 S H3 Serial input (I L )

17 7 ARITHMETIC LOGIC SHIFT UNIT Shift Microoperations S3 S2 S S B i A i A i- A i+ C i Arithmetic Circuit C 4 x Logic Circuit D i Select i+ i 2 3 E i shr shl F S3 S2 S S Cin Operation Function F = A Transfer A F = A + Increment A F = A + B Addition F = A + B + Add with carry F = A + B Subtract with borrow F = A + B + Subtraction F = A - Decrement A F = A TransferA X F = A B AND X F = A B OR X F = A B XOR X F = A Complement A X X X X X X F = shr A F = shl A Shift right A into F Shift left A into F