Section 2 - Background
Installation and Operation Manual
Brooks RS485 L-Protocol MFCs
2.3. Message Format
X-DPT-RS485-GF100-Series-MFC-eng
Part Number: 541B183AAG
March, 2020
Messages on the bus are sent as packets with a fixed format, illustrated as
the following diagram. Each packet begins with the target digital MFC
controller MAC ID (address), an STX character (0x02), a service (command)
code (0x80 for read and 0x81 for write), a packet length character, a
variable identifier (consisting of Class ID, Instance ID, Attribute ID) and a
data count between 0 to 2. Each packet ends with a pad byte of 0, and a 1-
byte checksum, which is the sum of all of the bytes in the packet, other than
the target MAC ID, modulo 256. The checksum calculation discards the
carry from the byte summation calculation. This message structure
resembles with the one used by DeviceNet protocol.
MAC ID (Targeted MFC Controller Address)
STX(0x02)
Command Code(0x80 for read, 0x81 for write)
Packet Length
Class ID
Instance ID
Attribute ID
Data(0 - 2 bytes)
Pad(0x00)
Checksum
All communication on the bus is done by service requests (from Master
controller to a specified MFC slave controller), each addressed to a specific
MAC ID, Class ID, Instance ID and Attribute ID. Currently this protocol
supports only 2 services
– Read and Write.
All communication on the bus is done by service requests (from Master
controller to a specified MFC slave controller), each addressed to a specific
MAC ID, Class ID, Instance ID and Attribute ID. Currently this protocol
supports only 2 services
– Read and Write.
The following table summarizes the specification of Class ID, Instance ID
and Attribute ID for each supported message:
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