Comtech EF Data SFC1800A - Manual (Page 45)

SFC1800A Synthesized Frequency Upconverter User Interfaces
TM111 – Rev. 1.0 4-21
4.4.2.2 RLLP Protocol Wrapper
The Radyne COMMSPEC is byte-oriented, with the Least Significant Bit (LSB) issued first. Each
data byte is conveyed as mark/space information with two marks comprising the stop data. When
the last byte of data is transmitted, a hold comprises one steady mark (the last stop bit). To begin
or resume data transfer, a space substitutes this mark. This handling scheme is controlled by the
hardware and is transparent to the user. A pictorial representation of the data and its surrounding
overhead may be shown as follows:
S1 S2 B
0
B
1
B
2
B
3
B
4
B
5
B
6
B
7
S1 S2,
etc.
The stop bits, S1 and S2, are each a mark. Data flow remains in a hold mode until S2 is replaced
by a space. If S2 is followed by a space, it is considered a start bit for the data byte and not part
of the actual data (B
0
- B
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:
- the message format header character, or ASCII sync character, that defines the
beginning of a message. The character value is always 16h.
- the Byte Count is the number of bytes in the field, ranging from 0 -
TBD.
- the Source Identifier defines the message originator’s multidrop address.
Note that all nodes on a given control bus have a unique address that
must be defined.
- The Destination Identifier specifies the multidrop address of the device(s)
to which the message is sent.
- The FSN is a tag with a value from 0 - 255 that is sent with
each message. It assures sequential information framing and correct equipment
acknowledgment and data transfers.
- 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 SFC1800A protocol.