Simulink Reference    
Bitwise Logical Operator

Logically mask, invert, or shift the bits of an unsigned integer signal

Library

Math Operations

Description


The Bitwise Logical Operator performs any of a set of logical masking (AND, OR, XOR), inversion (NOT), and shifting (SHIFT_LEFT, SHIFT_RIGHT) operations on the bits of an unsigned integer signal. The block's parameter dialog lets you choose the operation to perform. You can use the Bitwise Logical Operator block to perform bitwise operations on arrays of unsigned integer signals.

Masking Operations

The Bitwise Logical Operator's masking operations (AND, OR, XOR) logically combine each bit of the input signal with the corresponding bit of a constant operand called the mask. You specify the mask's value and the logical operation via the block's parameter dialog. The mask and the logical operation determine the value of each bit of the output signal as follows.

Operation
 Mask Bit
 Input Bit
 Output Bit
AND
 1
 1
 1

1
 0
 0

0
 1
 0

0
 0
 0
OR
 1
 1
 1

0
 1
 1

1
 0
 1

0
 0
 0
XOR
 1
 1
 0

1
 0
 1

0
 1
 1

0
 0
 0

A Bitwise Operator block accepts arrays for both signals and masks. In general, the mask must have the same dimensionality as the input signal, i.e., a 5-by-4 input signal requires a 5-by-4 mask. The block applies each element of the mask to the corresponding input element. The following exceptions exist to the general rule that the input and the mask must have the same dimensionality:

When selecting a masking operation, use the Second operand field of the block's parameter dialog to specify the mask or masks. You can enter any MATLAB expression that evaluates to a scalar, matrix, or cell array. Use strings in your mask expression to specify hexadecimal values (e.g., 'FFFF').

If necessary, the block truncates the high-order bits of the mask value to fit the word size of the input signal's data type. For example, suppose you specify the mask value as 'FF00' and the input signal is of type uint8. The block truncates the specified value to '00'.

You can use matrices to specify hexadecimal masks, but beware of the pitfalls of such an approach. For example, the MATLAB expression['00' 'FF'] represents a single string 'FF00' rather than two strings. Similarly, the expression ['FFFF'; '0000'] represents two strings but the expression ['FFFF'; '00'] is invalid and hence causes MATLAB to signal an error. You can avoid these pitfalls by always using cell arrays to specify hexadecimal values, or to mix decimal and hexadecimal values, for masks. For example, the following model

uses a cell array ({'F0' '0F'}) to specify hexadecimal values for the masks for a two-element input vector.

Inversion Operation

The Bitwise Logical Operator's NOT operation inverts the bits of the input signal. In particular, it performs a one's complement operation on the input signal to produce an output signal each of whose bits is 1 if the corresponding input bit is 0 and vice versa.

Shift Operations

The Bitwise Logical Operator's shift operations, SHIFT_LEFT and SHIFT_RIGHT, shift the bits of the input signal left or right to produce the output signal. You specify the amount of the shift in the Second operand field of the block's parameter dialog. If you specify a shift amount that is greater than the word size of the input signal, the block uses the input word size as the shift amount, resulting in a zero output signal. The dimensionality rules that apply to masks and inputs also apply to shift factors and inputs.

Data Type Support

The Bitwise Logical Operator accepts real-valued inputs of any of the unsigned integer data types: uint8, uint16, uint32. All the elements of a vector input must be of the same data type. The output signal is of the same data type as the input.

Parameters and Dialog Box

Bitwise operator
Specifies the bitwise operator applied to the input signal.
Second operand
Specifies the mask operand for masking operations and the shift amount for shift operations. You can enter any MATLAB expression that evaluates to a scalar, matrix, or cell array. If the block input is an array, the block applies each parameter value to the corresponding element of the input. If the input is a scalar, the block outputs an array, each of whose elements is the result of applying the corresponding parameter value to the input. (If the Bitwise operator is NOT, this parameter does not appear.)

Characteristics

Sample Time
 Inherited from driving block
Scalar Expansion
 Of inputs and Second operand parameter
Dimensionalized
 Yes
States
 None
Zero Crossing
 No
Direct Feedthrough
 Yes


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