Comtech EF Data RCS20 - Manual (Page 144)

RCS20 M:N Redundancy Switch Revision 15
Remote Operations MN-RCS20 and CD-RCS20
A–2
A.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 one mark 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
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 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 = 00010110b. 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, ranging from 0 through
TBD, (2 bytes).
- the Source Identifier defines the message originator’s multi-drop address, (1 byte).
IMPORTANT
All nodes on a given control bus have a unique address that must be defined.
- The Destination Identifier specifies the multi-drop address of the device(s) to which
the message is sent, (1 byte).