Grass Valley XSwitch Feb 01 2005 - Manual (Page 36)

©2001 XSWITCH Installation and Operations Manual 35
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EXAMPLE FOR BASIC PROGRAM V 2.0:
Known command string to send: “2,L”
LEN is length of command string.
Known values:
DEST: 04 decimal value —> convert to ASCII character of value: 04
SRC: 254 decimal value —> convert to ASCII character of value: 254
LEN: 03 decimal value —> convert to ASCII character of value: 03
Input string for CRC program: Chr$(4)+Chr$(254)+Chr$(3)+”2,L”
Returned hexadecimal CRC value returned from basic program under Visual Basic: “FFFFFA92”
LSB needed from CRC is 92
MSB needed from CRC is FA
Using the standard protocol:
Where the CRCL is the LSB needed from CRC and the CRCH is the MSB needed from CRC,
the entire packet is now in the form (using values from previous example):
packet string = Chr$(4)+Chr$(254)+Chr$(3)+”2,L”+Chr$(&H92)+Chr$(&HFA)
NOTES: LSB and MSB of CRC are hexadecimal values. Remember to change back to decimal
form to use Chr$ or use hexadecimal notation.
Basic eliminates leading zeros. Therefore if CRC returns only 3 characters, the last two are LSB
and the first character from CRC is MSB.
i.e.: CRC=“3FE”, LSB=FE MSB=3
i.e.: CRC=“2E”, LSB=2E MSB=0
DEST SRC LEN C/C DATA1 … DATAn CRCL CRCH