Comtech-ef-data MD2401 Instrukcja Użytkownika Pobierz pdf (Strona 43)

MD2401 L-Band Multi Demod Installation and Operation Manual User Interfaces

MN-MD2401 4–11

Revision 7

The COMMSPEC developed for use with the Radyne Link Level Protocol (RLLP) organizes the

actual monitor and control data within a shell, or ‘protocol wrapper’, that surrounds the data. The

format and structure of the COMMSPEC message exchanges are described herein. Decimal

numbers have no suffix; hexadecimal numbers end with a lower case h suffix and binary values

have a lower case b suffix. Thus, 22 = 16h = 000010110b. The principal elements of a data

frame, in order of occurrence, are summarized as follows:

<SYNC> - the message format header character, or ASCII sync character, that defines the beginning of a

message. The <SYNC> character value is always 16h (1 Byte).

<BYTE COUNT> - the Byte Count is the number of bytes in the <DATA> field (two bytes).

<SOURCE ID> - the Source Identifier defines the multi-drop address origin. Note that all nodes on a

given control bus have a unique address that must be defined (1 Byte).

<DESTINATION ID> - The Destination Identifier serves as a pointer to the multi-drop destination device

that indicates where the message is to be sent (1 Byte).

<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 (1 Byte).

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

with the data that follows it. Equipment under MCS control recognizes this code via firmware

identification and subsequently steers the DATA accordingly to perform a specific function or

series of functions. Acknowledgment and error codes are returned in this field (two bytes).

<...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

<SYNC> character (1 Byte). The checksum determines the presence or absence of errors

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

computed as shown in Table 4-4 below.

Table 4-2. Checksum Calculation Example

Byte Field

Data Content

Running

Checksum

(Byte 1)

00h = 00000000b

00000000b

(Byte 2)

02h = 00000010b

00000010b

F0h = 11110000b

11110010b

<DESTINATION

ID>

2Ah = 00101010b 00011100b

<FSN>

09h = 00001001b

00100101b

<OPCODE> (Byte

00h = 00000000b

00100101b

<OPCODE> (Byte

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:

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 105 106

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