APPENDIX D
4618-021
142
CRC GENERATION
A sixteen bit cyclic redundancy code ( CRC ) is used in preference to the more common checksum technique to
minimize the possibility of the detector responding to a corrupted transmission.
Method
A sixteen bit CRC accumulator is used, the data being transmitted over the link is four bytes of ASCII encoded
hexadecimal with no leading zero suppression.
Polynomial used,
G(x) = x
16
+ x
12
+ x
5
+ 1 (i.e CCITT)
Data is processed Least Significant Disc (LSB) of character first and transmitted high byte and high nibble to low
byte and low nibble.
The CRC accumulator is initialized to FFFF before every packet is started.
Example CRC Numbers.
MESSAGE STRING
CRC (HEX)
T
1B26
THE
44BE
THE,QUICK,BROWN,FOX,0123456789
DF91
Note: The CRC does not include the terminating null character in the above strings.
Refer to the following C Program for a straightforward non-optimized CRC-CCITT routine.
Содержание Signature
Страница 16: ......
Страница 26: ...INSTALLATION 10 4618 021 Fig 5 Typical Metal Detector Conveyor ...
Страница 31: ...INSTALLATION 4618 021 15 Fig 10 Cable Gland Assemblies for Power Supply Unit ...
Страница 52: ...OPERATING INSTRUCTIONS 36 4618 021 Fig 14 Supervisor Mode Flow Chart ...
Страница 55: ...OPERATING INSTRUCTIONS 4618 021 39 Fig 15 Engineer Mode Flow Chart ...
Страница 71: ...OPERATING INSTRUCTIONS 4618 021 55 Fig 16 Pack Sensor Mode Flow Chart ...
Страница 82: ...OPERATING INSTRUCTIONS 66 4618 021 Fig 18 QA Inspector And Operator Flow Chart ...
Страница 92: ...OPERATING INSTRUCTIONS 76 4618 021 Fig 19 Viewing Mode Flow Chart ...