Protocol Wrapper - Radyne DMD20 Installation And Operation Manual

User Interfaces
Each piece of earth station equipment on a control bus has a unique physical address, which is
assigned during station setup/configuration or prior to shipment. Valid decimal addresses on one
control bus range from 032 through 255 for a total of up to 224 devices per bus. Address 255 of
each control bus is usually reserved for the M&C computer.

4.9.1.2 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 (00h) 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
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
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:
<SYN>:
<BYTE COUNT>:
<SOURCE ID>:
<DESTINATION ID>:
<FRAME SEQUENCE NUMBER>:
4-46
B B B
1 2 3
- B ). The COMMSPEC developed for use with the Radyne Link
0 7
The message format header character, or ASCII sync
character, that defines the beginning of a message. The
<SYN> character value is always 16h.
The Byte Count is the number of bytes in the <DATA>
field, ranging from 0 through 255 for the DMD20 protocol
(1 Byte), or ranging from 0 through 509 for the DMD20
protocol (2 Bytes).
The Source Identifier defines the multi-drop address
origin.
Note: All nodes on a given control bus have a
unique address that must be defined.
The Destination Identifier serves as a pointer to the
multi-drop destination device that indicates where the
message is to be sent.
The Frame Sequence Number (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.
DMD20 Universal Satellite Modem
B B B
4 5 6
B S1 S2,
7
etc.
TM103 - Rev. 1.1