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Logic Micro Operation

The document discusses register transfer and micro-operations. It covers register transfer language, register transfer, bus and memory transfers, and different types of micro-operations including arithmetic, logic, and shift micro-operations. It provides examples of logic and shift micro-operations and their applications in manipulating bits in registers. The hardware implementation of shift micro-operations using an arithmetic logic and shift unit is also described.

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Register Transfer and Micro-operations 1 CSE 211 Overview  Register Transfer Language  Register Transfer  Bus and Memory Transfers  Arithmetic Micro-operations  Logic Micro-operations  Shift Micro-operations  Arithmetic Logic Shift Unit
Register Transfer and Micro-operations 2 CSE 211 Logic Micro operations
Register Transfer and Micro-operations 3 CSE 211 Logic Microoperations
Register Transfer and Micro-operations 4 CSE 211 Hardware Implementation 0 0 F = A  B AND 0 1 F = AB OR 1 0 F = A  B XOR 1 1 F = A’ Complement S1 S0 Output -operation Function table B A S S F 1 0 i i i 0 1 2 3 4 X 1 MUX Select
Register Transfer and Micro-operations 5 CSE 211 Applications of Logic Microoperations  Logic microoperations can be used to manipulate individual bits or a portions of a word in a register  Consider the data in a register A. In another register, B, is bit data that will be used to modify the contents of A  Selective-set A  A + B  Selective-complement A  A  B  Selective-clear A  A • B’  Mask (Delete) A  A • B  Clear A  A  B  Insert A  (A • B) + C  Compare A  A  B
Register Transfer and Micro-operations 6 CSE 211 Applications of Logic Microoperations 1. In a selective set operation, the bit pattern in B is used to set certain bits in A 1 1 0 0 At 1 0 1 0 B 1 1 1 0 At+1 (A  A + B) If a bit in B is set to 1, that same position in A gets set to 1, otherwise that bit in A keeps its previous value 2. In a selective complement operation, the bit pattern in B is used to complement certain bits in A 1 1 0 0 At 1 0 1 0 B 0 1 1 0 At+1 (A  A  B) If a bit in B is set to 1, that same position in A gets complemented from its original value, otherwise it is unchanged
Register Transfer and Micro-operations 7 CSE 211 Applications of Logic Microoperations 3. In a selective clear operation, the bit pattern in B is used to clear certain bits in A 1 1 0 0 At 1 0 1 0 B 0 1 0 0 At+1 (A  A  B’) If a bit in B is set to 1, that same position in A gets set to 0, otherwise it is unchanged 4. In a mask operation, the bit pattern in B is used to clear certain bits in A 1 1 0 0 At 1 0 1 0 B 1 0 0 0 At+1 (A  A  B) If a bit in B is set to 0, that same position in A gets set to 0, otherwise it is unchanged
Register Transfer and Micro-operations 8 CSE 211 Applications of Logic Microoperations 5. In a clear operation, if the bits in the same position in A and B are the same, they are cleared in A, otherwise they are set in A 1 1 0 0 At 1 0 1 0 B 0 1 1 0 At+1 (A  A  B)
Register Transfer and Micro-operations 9 CSE 211 Applications of Logic Microoperations 6. An insert operation is used to introduce a specific bit pattern into A register, leaving the other bit positions unchanged This is done as – A mask operation to clear the desired bit positions, followed by – An OR operation to introduce the new bits into the desired positions – Example • Suppose you wanted to introduce 1010 into the low order four bits of A: • 1101 1000 1011 0001 A (Original) 1101 1000 1011 1010 A (Desired) • 1101 1000 1011 0001 A (Original) 1111 1111 1111 0000 Mask 1101 1000 1011 0000 A (Intermediate) 0000 0000 0000 1010 Added bits 1101 1000 1011 1010 A (Desired)
Register Transfer and Micro-operations 10 CSE 211 Shift Microoperations • There are three types of shifts – Logical shift – Circular shift – Arithmetic shift • What differentiates them is the information that goes into the serial input Serial input • A right shift operation • A left shift operation Serial input
Register Transfer and Micro-operations 11 CSE 211 Logical Shift • In a logical shift the serial input to the shift is a 0. • A right logical shift operation: • A left logical shift operation: • In a Register Transfer Language, the following notation is used – shl for a logical shift left – shr for a logical shift right – Examples: • R2  shr R2 • R3  shl R3 0 0
Register Transfer and Micro-operations 12 CSE 211 Circular Shift • In a circular shift the serial input is the bit that is shifted out of the other end of the register. • A right circular shift operation: • A left circular shift operation: • In a RTL, the following notation is used – cil for a circular shift left – cir for a circular shift right – Examples: • R2  cir R2 • R3  cil R3
Register Transfer and Micro-operations 13 CSE 211 Arithmetic Shift • An arithmetic shift is meant for signed binary numbers (integer) • An arithmetic left shift multiplies a signed number by two • An arithmetic right shift divides a signed number by two • Sign bit : 0 for positive and 1 for negative • The main distinction of an arithmetic shift is that it must keep the sign of the number the same as it performs the multiplication or division • A right arithmetic shift operation: • A left arithmetic shift operation: 0 sign bit sign bit
Register Transfer and Micro-operations 14 CSE 211 Arithmetic Shift • An left arithmetic shift operation must be checked for the overflow 0 V Before the shift, if the leftmost two bits differ, the shift will result in an overflow • In a RTL, the following notation is used – ashl for an arithmetic shift left – ashr for an arithmetic shift right – Examples: » R2  ashr R2 » R3  ashl R3 sign bit
Register Transfer and Micro-operations 15 CSE 211 Hardware Implementation of Shift Microoperation
Register Transfer and Micro-operations 16 CSE 211 Arithmetic Logic and Shift Unit Arithmetic Circuit Logic Circuit C C 4 x 1 MUX Select 0 1 2 3 F S3 S2 S1 S0 B A i A D A E shr shl i+1 i i i i+1 i-1 i i S3 S2 S1 S0 Cin Operation 0 0 0 0 0 F = A 0 0 0 0 1 F = A + 1 0 0 0 1 0 F = A + B 0 0 0 1 1 F = A + B + 1 0 0 1 0 0 F = A + B’ 0 0 1 0 1 F = A + B’+ 1 0 0 1 1 0 F = A - 1 0 0 1 1 1 F = A 0 1 0 0 X F = A  B 0 1 0 1 X F = A B 0 1 1 0 X F = A  B 0 1 1 1 X F = A’ 1 0 X X X F = shr A 1 1 X X X F = shl A