Comtech EF Data CDM-550T - Manual (Page 120)

CDM-550T Satellite Modem Revision 3
Remote Control MN/CDM550T.IOM
15.5.4 Instruction Code Qualifier
This is a single character which 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
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’
?
(ASCII code 63)
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’.
2. From Target to Controller, the only permitted values are:
=
(ASCII code 61)
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).
?
(ASCII code 63)
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.
!
(ASCII code 33)
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!
*
(ASCII code 42)
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 valid, BUT the modem will not permit
that particular parameter to be changed at that time, the target will acknowledge
the message by replying, for example, with TFQ* (with no message arguments).
15.5.5 Message Arguments
Arguments are not required for all messages. Arguments are ASCII codes for the characters 0 to 9
(ASCII 48 to 57); A to Z (ASCII 65 to 90); period (ASCII 46); and comma (ASCII 44).
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