Comtech EF Data CDM-550T - Manual (Page 119)

CDM-550T Satellite Modem Revision 3
Remote Control MN/CDM550T.IOM
Target-to-Controller:
Start of
Packet
Target
Address
Address
De-limiter
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}
Each of the components of the packet is now explained.
15.5.1 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.
15.5.2 Address
Up to 9,999 devices can be uniquely addressed. In RS-232 applications this value is set to 0. In
RS-485 applications, the permissible range of values is 1 to 9999. It is programmed into a target
unit using the front panel keypad.
Important note: The controller sends a packet with the address of a target - the destination of the
packet. When the target responds, the address used is the same address, to indicate to the
controller the source of the packet. The controller does not have its own address.
15.5.3 Instruction Code
This is a three-character alphabetic sequence which identifies the subject of the message.
Wherever possible, the instruction codes have been chosen to have some significance. For
example TFQ for transmit frequency, RMD for receive modulation type, etc. This aids in the
readability of the message, should it be displayed in its raw ASCII form. Only upper case
alphabetic characters may be used (A-Z, ASCII codes 65 - 90).
15–3