Beijer Electronics SCOM Protocol EN - Manual (Page 16)

Protocol Description and Timings
16 Elektronik-Systeme Lauer, MAEN976
5 Protocol Description and Timings
The protocol used for transferring SCOM messages and receiving response messages
is optimized for easy software implementation. Regardless of the type of interface, a
connected monitor is always passive and listening for a command to be received by
any available communication interface. A monitor never sends SCOM messages by
itself, unless it is configured as a remote controller.
If a monitor receives a SCOM message from any interface, it verifies the message and
checks the address field ADR. In case of an address match between the received ad-
dress and the monitor address, the command is processed.
If the broadcast address 0xFF is received, a command is always processed by any
monitor in the network. Depending on the received address and the type of the in-
terface, a response message (ACK or NAK) might be sent back to the interface, from
which the command was received.
If a monitor is individually addressed and a serial port (RS232 or RS485) is used, the
next command shall not be sent until a delay time called Inter-message gap. The
Inter-message gap depends on the baud rate and is calculated as shown below:
Example
Inter-message gap at 9600 baud: Ti = 5 x 10 / 9600
≈ 0.0052 s = 5.2 ms
5 x 10
Ti =
b
Ti: Inter-message gap [s]
b: Baud rate [bits/second]