2 packet structure – Comtech EF Data CDM-570A User Manual
Page 243
CDM-570A/570AL Satellite Modem with Optional Packet Processor
MN-CDM570A
Serial-based Remote Product Management
Revision 2
8–3
All messages from Controller-to-Target require a response, with one exception: 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. The exception to
this is when the Controller broadcasts a message (such as Set Time/Date) using Address 0, when the Target is set to EIA-485 mode.
8.2.2
Packet Structure
The exchange of information is transmitted, Controller-to-Target and Target-to-Controller, in ‘packets’. Each packet contains a finite
number of bytes consisting of printable ASCII characters, excluding ASCII code 127 (DELETE).
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.
Controller-to-Target
Start of Packet
Target Address
Address Delimiter
Instruction Code
Code Qualifier
Optional Arguments
End of Packet
<
ASCII code 60
(1 character)
(4 characters)
/
ASCII code 47
(1 character)
(3 characters)
= or ?
ASCII codes 61 or 63
(1 character)
(n characters)
Carriage Return
ASCII code 13
(1 character)
Packet “issued command” example: <0000/RSW=32[cr]
Packet “issued query” example:
<0000/RSW?[cr]
Target-to-Controller
Start of Packet
Target Address
Address Delimiter
Instruction Code
Code Qualifier
Optional Arguments
End of Packet
>
ASCII code 62
(1 character)
(4 characters)
/
ASCII code 47
(1 character)
(3 characters)
=, ?, !, or *
ASCII codes
61, 63, 33, or 42
(1 character)
(From 0 to n characters)
Carriage Return, Line
Feed
ASCII codes 13,10
(2 characters)
Packet example – response received for issued query: >0000/RSW=32[cr][lf]
Detailed description of the packet components follow.