REGISTER TRANSFER LANGUAGE MICROOPERATIONS

• Logic Microoperations • Shift Microoperations TODAY OUTLINES • Logic Microoperations • Shift Microoperations

LOGIC MICROOPERATIONS

LOGIC MICROOPERATIONS Specify binary operations on the strings of bits in registers Logic microoperations are bit-wise operations, i.e., they work on the individual bits of data useful for bit manipulations on binary data useful for making logical decisions based on the bit value The symbols for the four basic logic operations are: OR (), AND (), XOR (), Complement/NOT

LOGIC MICROOPERATIONS v OR (SETS Bits) ^ AND (CLEARS Bits)  XOR (Complement Bits, 2 Sources) NOT (Complement Bits, 1 Source) Example: R3 R4 v R6 Example: R2 DR ^ R1 Example: PC PC  DR Example: R6 R1

LOGIC MICROOPERATIONS Example: Let R1 = 10101010 and R2 = 11110000 After the operations, R0 becomes:

HARDWARE IMPLEMENTATION OF LOGIC MICROOPERATIONS B i 1 4 X 1 F i MUX 2 3 Select S 1 S Function table 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

APPLICATIONS OF LOGIC MICROOPERATIONS Logic microoperations can be used to manipulate individual bits or a portions of a word in a register Logic microoperations can change bit values, clear a group of bits, or insert new bit values into a register.

AND microoperation Used for clearing one or more bits in a register to 0. Boolean equations: X • 0 = 0 When ANDed with 0, binary variable X produces 0. X • 1 = X When ANDed with 1, binary variable X remains unchanged.

AND microoperation X • 0 = 0 X • 1 = X Example: 10101101 10101011 R1 (data) 00000000 11111111 R2 (mask) 00000000 10101011 R1  R1 ^ R2 AND operation: Selectively clear bits of a register Masking out the bits X • 1 = X R1 : High-order byte = Clear Low-order byte = Unchanged

OR microoperation Used to set one or more bits in a register. Boolean equations: X + 1 = 1 When ORed with 1, binary variable X produces a 1. X + 0 = X When ORed with 0, binary variable X remains unchanged.

OR microoperation X + 1 = 1 X + 0 = X Example: 10101101 10101011 R1 (data) 11111111 00000000 R2 (mask) 11111111 10101011 R1  R1 v R2 OR operation: Selectively set bits of a register R1: High-order byte = Set to 1’s Low-order byte = Unchanged

XOR microoperation Used to complement one or more bits in a register. Boolean equations: X  1 = X When XORed with 1, binary variable X complemented. X  0 = X When XORed with 0, binary variable X remains unchanged.

XOR microoperation X  1 = X X  0 = X Example: 10101101 10101011 R1 (data) 11111111 00000000 R2 (mask) 01010010 10101011 R1  R1  R2 XOR operation: Selectively complement bits of a register R1: High-order byte = Complemented Low-order byte = Unchanged

SHIFT MICROOPERATIONS

SHIFT MICROOPERATIONS Shift microoperations are used for: Lateral movement of data. Serial transfer of data. Manipulating the contents of registers in arithmetic, logical, and control operations. Left shift : toward the MSB Right shift : toward the LSB MSB 7 6 5 4 3 2 1 LSB

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/incoming bit A right shift operation A left shift operation LSB Serial input Serial input MSB

SHIFT MICROOPERATIONS A right shift operation A left shift operation LSB Serial input MSB Serial input

SHIFT MICROOPERATIONS In RTL, string of letters are used to specify 1-bit shift operations: Shift left : sl Shift right : sr

Shift Microoperations LOGICAL SHIFT Assume the serial input/incoming bit to the shift is a 0. A right shift operation: A left shift operation: Example of Shifts: Type Symbolic Source R2 After Shift: Designation Destination R1 Shift Left R1 sl R2 10011110 00111100 Shift Right R1 sr R2 11100101 01110010

SHIFT MICROOPERATIONS Example 1: Let R2 = 11001001 After the Shift operation, R1 becomes: Note: These shifts "zero fill". Sometimes a separate flip-flop is used to provide the data shifted in, or to “catch” the data shifted out.