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The two basic types are the arithmetic left shift and the arithmetic right shift. For binary numbers it is a bitwise operation that shifts all of the bits of its operand; every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in.
The very fastest shifters are implemented as full crossbars, in a manner similar to the 4-bit shifter depicted above, only larger. These incur the least delay, with the output always a single gate delay behind the input to be shifted (after allowing the small time needed for the shift count decoder to settle; this penalty, however, is only incurred when the shift count changes).
Verilog was later submitted to IEEE and became IEEE Standard 1364-1995, commonly referred to as Verilog-95. In the same time frame Cadence initiated the creation of Verilog-A to put standards support behind its analog simulator Spectre. Verilog-A was never intended to be a standalone language and is a subset of Verilog-AMS which encompassed ...
Left arithmetic shift Right arithmetic shift. In an arithmetic shift, the bits that are shifted out of either end are discarded. In a left arithmetic shift, zeros are shifted in on the right; in a right arithmetic shift, the sign bit (the MSB in two's complement) is shifted in on the left, thus preserving the sign of the operand.
ALU shift operations cause operand A (or B) to shift left or right (depending on the opcode) and the shifted operand appears at Y. Simple ALUs typically can shift the operand by only one bit position, whereas more complex ALUs employ barrel shifters that allow them to shift the operand by an arbitrary number of bits in one operation. In all ...
P = 0000 0110 0. Arithmetic right shift. P = 0000 0110 0. The last two bits are 00. P = 0000 0011 0. Arithmetic right shift. P = 0000 0011 0. The last two bits are 10. P = 1101 0011 0. P = P + S. P = 1110 1001 1. Arithmetic right shift. P = 1110 1001 1. The last two bits are 11. P = 1111 0100 1. Arithmetic right shift. The product is 1111 0100 ...
As "data in" presents 1,0,1,1,0,0,0,0 (in that order, with a pulse at "data advance" each time—this is called clocking or strobing) to the register, this is the result. The right hand column corresponds to the right-most flip-flop's output pin, and so on. So the serial output of the entire register is 00010110.
The straight ring counter has the logical structure shown here: Instead of the reset line setting up the initial one-hot pattern, the straight ring is sometimes made self-initializing by the use of a distributed feedback gate across all of the outputs except that last, so that a 1 is presented at the input when there is no 1 in any stage but the last.