Comtech EF Data SDM-2020 - Manual (Page 172)

SDM-2020 Satellite Modulator Revision 7
Remote Control Operation MN/SDM2020M.IOM
A-2
The general message structure is as follows:
• Start Character
• Device Address ‘add’
• Command/Response
• End of Message Character
If a command is issued remotely with the intent to change a modulator configurable
parameter, the ‘REM_’ command must be issued first. This is to avoid data collision if
one was to be changing data from the front panel while another was sending a remote
command at the same time.
The first exception to the rule is if a command was issued to check a parameter status.
The ‘REM_’ command would not be required first and a status would be returned
normally.
The second exception to this rule is if the ‘MCP_’ command is issued for program
configuration changes or a status request. When this particular command is issued with a
command string attached, the Modulator will automatically engage remote mode,
followed by the execution of the ‘MCP_’ command. While this command is being
processed, any key presses from the front panel are stored in a keyboard buffer and
executed after the MCP command is completed.
A.1.1 S
TART
C
HARACTER
A single character precedes all messages transmitted on the remote link. This
character flags the start of a message. This character is:
• “<” for commands
• “>” for responses
A.1.2 D
EVICE
A
DDRESS
The device address is the address of the one satellite modulator which is
designated to receive a transmitted command, or which is responding to a
command.
Note: Address 0 is reserved as a global address which simultaneously addresses all
devices on a given communications link.
Valid device addresses are 1 to 3 characters long, and in the range of 1 to 255.
Devices do not acknowledge global commands.
Each satellite modulator, which is connected to a common remote
communications link, must be assigned its own unique address. Addresses are
software selectable at the modulator, and must be in the range of 1 to 255.