Mocomtech CDM-QX - Manual (Page 220)

CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision 7
Appendix C MN/CDMQX.IOM
C–2
• Target-to-Controller pair has one line receiver (Controller), and all Targets have Tri-State
drivers.
C.3 EIA-232
This is a much simpler configuration in which the Controller device is connected directly to the
Target via a two-wire-plus-ground connection. Controller-to-Target data is carried, via EIA-232
electrical levels, on one conductor, and Target-to-Controller data is carried in the other direction
on the other conductor.
C.4 Basic Protocol
Whether in EIA-232 or EIA-485 mode, all data is transmitted as asynchronous serial characters,
suitable for transmission and reception by a UART. In this case, the asynchronous character
format is fixed at 8N1. The baud rate may vary between 1,200 and 38,400 baud.
All data is transmitted in framed packets. The Controller is assumed to be a PC or ASCII dumb
terminal, which is in charge of the process of monitor and control. The Controller 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.
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.
C.5 Packet Structure
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)
Example: < 0135/TRQ=70.2345{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)
Example: > 0654/RSW=32{CR} {LF}