Construct CRC generator object

`h = crc.generator(polynomial)`

`h = crc.generator(detectorObj)`

```
h = crc.generator(‘Polynomial', polynomial,
‘param1', val1, etc.)
```

`h = crc.generator`

`h = crc.generator(polynomial)`

constructs
a CRC generator object H defined by the generator polynomial POLYNOMIAL.

`h = crc.generator(detectorObj)`

constructs
a CRC generator object H defined by the parameters found in the CRC
detector object DETECTOROBJ.

`h = crc.generator(‘property1', val1, ...)`

constructs
a CRC generator object H with properties as specified by the PROPERTY/VALUE
pairs.

`h = crc.generator`

constructs a CRC generator
object H with default properties. It constructs a CRC-CCITT generator,
and is equivalent to: h = crc.generator('Polynomial', '0x1021', 'InitialState',
'0xFFFF', ...

'ReflectInput', false, 'ReflectRemainder', false, 'FinalXOR', '0x0000').

The following table describes the properties of a CRC generator
object. All properties are writable, except `Polynomial`

.

Property | Description |
---|---|

`Polynomial` | The generator polynomial that defines connections for a linear feedback shift register. This property can be specified as a binary vector representing descending powers of the polynomial. In this case, the leading '1' of the polynomial must be included. It can also be specified as a string, prefaced by '0x', that is a hexadecimal representation of the descending powers of the polynomial. In this case, the leading '1' of the polynomial is omitted. |

`InitialState` | The initial contents of the shift register. This property can be specified as a binary scalar, a binary vector, or as a string, prefaced by '0x', that is a hexadecimal representation of the binary vector. As a binary vector, its length must be one less than the length of the binary vector representation of the Polynomial. |

`ReflectInput` | A Boolean quantity that specifies whether the input data should be flipped on a bytewise basis prior to entering the shift register. |

`ReflectRemainder` | A Boolean quantity that specifies whether the binary output CRC checksum should be flipped around its center after the input data is completely through the shift register. |

`FinalXOR` | The value with which the CRC checksum is to be XORed just prior to being appended to the input data. This property can be specified as a binary scalar, a binary vector, or as a string, prefaced by '0x', that is a hexadecimal representation of the binary vector. As a binary vector, its length must be one less than the length of the binary vector representation of the Polynomial. |

For information pertaining to the CRC generation algorithm, refer to the CRC Non-Direct Algorithm section of the Communications System Toolbox™ User's Guide.

encoded = generate(h, msg) generates a CRC checksum for an input message using the CRC generator object H. It appends the checksum to the end of MSG. The binary-valued MSG can be either a column vector or a matrix. If it is a matrix, then each column is considered to be a separate channel.

The following examples demonstrate the use of this object.

% Construct a CRC generator with a polynomial defined % by x^4+x^3+x^2+x+1: h = crc.generator([1 1 1 1 1])

% Construct a CRC generator with a polynomial defined % by x^4+x^3+x^2+x+1, all-ones initial states, reflected % input, and all-zeros final XOR value: h = crc.generator('Polynomial', '0xF', 'InitialState', ... '0xF', 'ReflectInput', true, 'FinalXOR', '0x0')

% Create a CRC-16 CRC generator, then use it to generate % a checksum for the % binary vector represented by the ASCII sequence '123456789'. gen = crc.generator('Polynomial', '0x8005', ... 'ReflectInput', true, 'ReflectRemainder', true); % The message below is an ASCII representation of ... % the digits 1-9 msg = reshape(de2bi(49:57, 8, 'left-msb')', 72, 1); encoded = generate(gen, msg);

% Construct a CRC generator with a polynomial defined % by x^3+x+1, with zero initial states, % and with an all-ones final XOR value: h = crc.generator('Polynomial', [1 0 1 1], ... 'InitialState', [0 0 0], ... 'FinalXOR', [1 1 1])

Was this topic helpful?