Radyne ComStream DM240-DVB Installation And Operation Manual page 37

High-speed digital modulator

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User Interfaces

<SYN> - the message format header character, or ASCII sync character, that defines the

beginning of a message. The <SYN> character value is always 16h.

<BYTE COUNT> - the Byte Count is the number of bytes in the <DATA> field, ranging from 0

through TBD. This field is 2 bytes long for the DM240 protocol.

<SOURCE ID> - the Source Identifier defines the message originator's multidrop address.

All nodes on a given control bus have a unique address that must be

defined.

<DESTINATION ID> - The Destination Identifier specifies the multidrop address of the device(s)

to which the message is sent.

<FRAME SEQUENCE NUMBER> - The FSN is a tag with a value from 0 through 255 that is sent

with each message. It assures sequential information framing and correct equipment

acknowledgment and data transfers.

<OPCODE> - The Operation Code field contains a number that identifies the message type

associated with the data that follows it. Acknowledgment and error codes are returned in this

field. This field is 2 Bytes for the DM240 protocol.

<...DATA...> - The Data field contains the binary, data bytes associated with the

<OPCODE>. The number of data bytes in this field is indicated by the <BYTE COUNT> value.

<CHECKSUM> - The checksum is the modulo 256 sum of all preceding message bytes,

excluding the <SYN> character. The checksum determines the presence or absence of errors

within the message. In a message block with the following parameters, the checksum is

computed as shown below in Table 4-4.

BYTE FIELD

<BYTE COUNT> (Byte 1)

<BYTE COUNT> (Byte 2)

<FSN>

<OPCODE> (Byte 1)

<OPCODE> (Byte 2)

<DATA> (Byte 1)

<DATA> (Byte 2)

4-18

Table 4-4. Checksum Calculation Example

DATA CONTENT

00h = 00000000b

02h = 00000010b

F0h = 11110000b

2Ah = 00101010b

09h = 00001001b

00h = 00000000b

03h = 00000011b

DFh = 11011111b

FEh = 11111110b

DM240-DVB High-Speed Digital Modulator

RUNNING CHECKSUM

00000000b

00000010b

11110010b

00011100b

00100101b

00101000b

00000111b

00000101b

TM083 - Rev. 3.0

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