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CDM-625 Advanced Satellite Modem
Remote Control
D.6
Instruction Code
This is a three-character alphabetic sequence that 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).
D.6.1
Instruction Code Qualifier
This single character further qualifies the preceding instruction code. Code Qualifiers obey the
following rules:
1. From Controller to Target, the only permitted values are:
=
(ASCII code 61
?
(ASCII code 63)
2. From Target to Controller, the only permitted values are:
=
(ASCII code 61)
?
(ASCII code 63)
!
(ASCII code 33)
The = (ASCII code 61) is used as the assignment operator, and is used to
indicate that the parameter defined by the preceding byte should be set to the
value of the argument(s) that follow it. For example: In a message from
controller to target, TFQ=0070.0000 would mean 'set the Transmit frequency to
70 MHz'
The ? (ASCII code 63) is used as the query operator, and is used to indicate
that the target should return the current value of the parameter defined by the
preceding byte. For example: In a message from controller to target, TFQ?
would mean 'return the current value of the transmit frequency'.
The = code (target to controller) is used in two ways:
First, if the controller has sent a query code to a target (for example: TFQ?,
meaning 'what is the Transmit frequency?'), the target would respond with
TFQ=xxxx.xxxx, where xxxx.xxxx represents the frequency in question.
Second, if the controller sends an instruction to set a parameter to a particular
value, then, providing the value sent in the argument is valid, the target will
acknowledge the message by replying with TFQ= (with no message arguments).
The ? code (target to controller) is only used as follows:
If the controller sends an instruction to set a parameter to a particular value,
then, if the value sent in the argument is not valid, the target will acknowledge
the message by replying, for example, with TFQ? (with no message arguments).
This indicates that there was an error in the message sent by the controller.
The ! code (target to controller) is only used as follows:
If the controller sends an instruction code which the target does not recognize,
the target will acknowledge the message by echoing the invalid instruction,
followed by the ! character. Example: XYZ!
D–4
MN-0000036 (Ref MN/CDM625.IOM)
Revision 1
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