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Serial/Ethernet Communication (SCOM) Interface
IND100084-14
Operational Requirements
The following sections define the operational requirements.
Serial Message Failure
If serial messages stop being transmitted or are corrupt, the unit will remain at the last commanded
brightness.
Periodic Messages
Commands shall be transmitted to the unit at a repetition no faster than 4 Hz.
Sending Multiple Commands / Command Queue
To ensure all commands are transmitted and executed successfully on the unit, a delay between each
command in the queue shall be at least 500ms. Some internal commands require slightly longer to process
internally in the unit, than others.
Keep-alive Alarm
The "SWI" query can be used for keep-alive alarm logic in the application software on the computer. It is
recommended to limit this function to once a second (1000ms).
Individually Addressed Command Response Time
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 for Serial Mode only), except as specified herein.
Broadcast Command Response Time
In response to Serial mode RS-485 broadcast command messages, after the last byte of the command
message is received, all units will reply within the time period defined for Te, below. Further more, any gap
between these individual responses will be less than the Intermessage Gap, defined below.
Te = (Tr + Lr) * N, where
Lr = length of the ACK/NAK message response
Tr = response time
N = the total number of units*
*) As the units reply in order to their address, the units must be given subsequent addresses, starting at zero,
for N to equal the total number of units. If not, N = the highest unit a 1.
The maximum Lr for a selected command set are shown in the table below:
Command BRT BZZ ETC POT SNB
SWI SWK
TYP MCC
Lr
9
9
11
9
13
19
11
28
xx**
**)This command will vary in size, and response time is longer. Make sure ACK is received from all units
before sending a new command.
Example:
For the BRT command, and 8 units, this corresponds to Te = (2.5 * 10 + 9 * 10) * 8 / 9600 = 95.8 ms
Intermessage Gap - Serial Mode
Following an individually addressed command, the next command shall not be issued until at least Tg = 5
character periods after the ACK or NAK message received. At 9600, that is 5 * 10 / 9600 = 5.2ms.
Following the issue of a broadcast command message, the next command shall not be issued until at least
Tc = Te + Tg, where Te is as defined for Broadcast Command response and Tg is defined above.
