Address Delimiter; Instruction Code; Instruction Code Qualifier - Comtech EF Data CDM-750 Installation And Operation Manual

CDM-750 Advanced High-Speed Trunking Modem
Appendix D
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.
D.5.3

Address Delimiter

This is the "forward slash" character '/' (ASCII code 47).
D.5.4

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.5.5

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)
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).
D–4
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MN-CDM750