Packet Structure - Comtech EF Data CDM-840 Installation And Operation Manual

CDM-840 Remote Router
Appendix B
The Controller, which is in charge of the process of monitor and control, is the only device that is permitted to initiate, at will, the
transmission of data. Targets are only permitted to transmit when they have been specifically instructed to do so by the Controller.
All bytes within a packet are printable ASCII characters, less than ASCII code 127. In this context, the Carriage Return and Line Feed
characters are considered printable. With one exception, all messages from Controller-to-Target require a response – this will be either to return
data that has been requested by the Controller, or to acknowledge reception of an instruction to change the configuration of the Target.
B.4

Packet Structure

Start of Packet
<
ASCII code 60
(1 character)
Example: <0000/RSH=30[cr]
Start of Packet
>
ASCII code 62
(1 character)
Example: >0000/BBU=107[cr][lf]
B.4.1 Start of Packet
Controller-to-Target: This is the character '<' (ASCII code 60).
Target-to-Controller: This is the character '>' (ASCII code 62).
Because this is used to provide a reliable indication of the start of packet, these two characters may not appear anywhere else within the
body of the message.
Target Address Address Delimiter
/
ASCII code 47
(4 characters) (1 character)
Target Address Address Delimiter
/
ASCII code 47
(4 characters) (1 character)
Controller-to-Target
Instruction Code Code Qualifier
= or ?
ASCII codes 61 or
63
(3 characters) (1 character)
Target-to-Controller
Instruction Code Code Qualifier
=, ?, !, or *
ASCII codes
61, 63, 33, or 42
(3 characters) (1 character)
B–2
Revision 0
MN-CDM840
Optional Arguments End of Packet
Carriage Return
ASCII code 13
(n characters) (1 character)
Optional Arguments End of Packet
Carriage Return,
Line Feed
ASCII codes 13,10
(From 0 to n
characters) (2 characters)