Hatteland Display 20 inch - HM 20T07 MIL-H - Manual (Page 55)

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Serial Communication (SCOM) Interface
Communication Interface
IND100084-1
Serial Message Failure
If serial messages stop being transmitted or are corrupt, the unit will remain at the last commanded brightness.
Periodic Messages
The Brightness Command shall be transmitted to the unit at a repetition no faster than 4 Hz.
Fault Detection and Power Interruption Recovery
To support implementation of keep-alive alarm logic in application software on the computer, the Brightness
Command message output from the computer to the unit can be repeated once per second, driven by receiving valid
acknowledge messages from the unit. The keep-alive logic should tolerate intermittent loss of valid acknowledge
messages without activating an alarm.
Response Time
Individually Addressed Command Response
The unit will output the required response within Tr = 2.5 character periods after the last byte of a command message
is received (2.6mS at 9600 bit/sec), except as specified herein.
Elapsed Time Counter “ETC”
Note: This command is not available on pre Feb 2005 units.
The unit features an elapsed time counter which counts the total number of hours that the unit has been switched
on. The ETC command can be sent to the unit to acquire the elapsed time in hours. No data shall be sent with this
command. The unit will reply to this command with an ACK attention code. The DATA field will be set to a three byte
string, where the most significant byte is transmitted first.
The ETC has a limit on maximum 298.261 hours, equivalent to 34 years. When this number is reached, the ETC will
stop counting, and the ETC command will always reply with maximum number of hours.
Examples:
ETC Command:
0x07 0xFF 0x45 0x54 0x43 0x00 0x1D
Answer, two hours elapsed time:
0x06 0xFF 0x45 0x54 0x43 0x03 0x1B 0x00 0x00 0x02 0xFD