Beijer Electronics SCOM Protocol EN - Manual (Page 13)

Message Format and Description
Elektronik-Systeme Lauer, MAEN976 13
3 Message Format and Description
A SCOM message is a stream of bytes, containing the destination, type of message
and the corresponding data, if available. The complete stream is protected by two
checksums. Data transfer is initiated by sending a command message. Depending on
the command, a response message may be sent back. Some commands may contain
sub-commands and data, which are sent in the data field of the message.
SCOM Message Basic Format
Each field of the message is described in the following table:
Byte 0 1 2 3 4 5 6 7 ... 7 + [LEN]
Field
ATN ADR CMD LEN ICHKH DATA ICHKD
Byte Field Value Size Description
0 ATN
0x07 (BELL):
Command
0x06 (ACK):
Acknowledge
0x15 (NAK):
Negative
Acknowledge
1 byte
Identifies the start of a new message. The
type of message is given by its value. Data
transfer is always initiated by using the
Command message type. Depending on
the command, a response message of type
Acknowledge or Negative Acknowledge
may be sent back by the destination.
1 ADR
0x00 to 0xEF:
Monitor group/
address
0xFF:
Broadcast address
0xF0 to 0xFE:
Unused address
range
1 byte
Defines the destination of a command
message or the source of the response
message. A unique monitor group/address
can be assigned to each monitor in a
network, and then individually addressed
using this field. By default, all monitors
also support the Broadcast address and
can be controlled simultaneously. In this
case, no response messages are sent.
2
3
4
CMD
0x42 0x52 0x54:
“BRT”
0x4D 0x41 0x4E:
“MAN”
0x56 0x45 0x52:
“VER”
0x50 0x4F 0x54:
“POT”
0x4D 0x43 0x43:
“MCC”
0x54 0x59 0x50:
“TYP”
0x45 0x54 0x43:
“ETC”
0x4C 0x41 0x55:
“LAU”
3 bytes
Contains the main command supported in
the current firmware version.
Please refer to section Command
Reference for a description of commands
and sub-commands.