Comtech EF Data DMD2401/DMD2401L - Manual (Page 75)

User Interfaces DMD2401/DMD2401L/DMD2401 IBS/IDR Satellite Modem
4-36 TM065 – Rev. 3.3
S1 S2 B
0
B
1
B
2
B
3
B
4
B
5
B
6
B
7
S1 S2,
etc.
The stop bit, S1 is a mark. Data flow remains in a hold mode until S1 is replaced by a space. If
S1 is followed by a space, the space character is considered a start (ST) and not part of the actual
data (B
0
- B
7
).
The above byte-oriented protocol is standard for UART based serial communication ports such as
Workstation or Personal Computer (PC) COM ports. COM ports should be configured for 8 data
bits, no parity, and one stop bit. For example, for 9600-baud operation, COM ports should be
configured as:
9600, 8, N, 1
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:
- the message format header character, or ASCII sync character, that defines the
beginning of a message. The character value is always 16h (1 Byte).
- the Byte Count is the number of bytes in the field (two bytes).
- 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).
- The Destination Identifier serves as a pointer to the multi-drop destination
device that indicates where the message is to be sent (1 Byte).
-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).
- 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
. The number of data bytes in this field is indicated by the value.
- The checksum is the modulo 256 sum of all preceding message bytes,
excluding the 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.