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DM240XR High-Speed Digital Modulator User Interfaces

MN-DM240XR– Revision 13 4–33

Table 4-4. Checksum Calculation Example

BYTE FIELD DATA CONTENT RUNNING CHECKSUM

<BYTE COUNT> (Byte 1) 00h = 00000000b 00000000b

<BYTE COUNT> (Byte 2) 02h = 00000010b 00000010b

<SOURCEID> F0h = 11110000b 11110010b

<DESTINATION ID> 2Ah = 00101010b 00011100b

<FSN> 09h = 00001001b 00100101b

<OPCODE> (Byte 1) 00h = 00000000b 00101000b

<OPCODE> (Byte 2) 03h = 00000011b 00101000b

<DATA> (Byte 1) DFh = 11011111b 00000111b

<DATA> (Byte 2) FEh = 11111110b 00000101b

Thus, the checksum is 00000101b; which is 05h or 5 decimal. Alternative methods of

calculating the checksum for the same message frame are:

00h + 02h + F0h + 2Ah + 09h + 00h + 03h + DFh + FEh = 305h.

Since the only concern is the modulo 256 (modulo 100h) equivalent (values that can be

represented by a single 8-bit byte), the checksum is 05h.

For a decimal checksum calculation, the equivalent values for each information field are:

0 + 2 + 240 + 42 + 9 + 0 + 3 + 223 + 254 = 773;

773/256 = 3 with a remainder of 5. This remainder is the checksum for the frame.

5 (decimal) = 05h = 0101b = <CHECKSUM>

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