7.4 FC Protocol Message Framing Structure
7.4.1 Content of a Character (byte)
Each character transferred begins with a start bit. Then 8
data bits are transferred, corresponding to a byte. Each
character is secured via a parity bit. This bit is set at "1"
when it reaches parity. Parity is when there is an equal
number of 1s in the 8 data bits and the parity bit in total.
A stop bit completes a character, thus consisting of 11 bits
in all.
Figure 7.3 Content of a Character
7.4.2 Message Structure
Each message has the following structure:
1. Start character (STX)=02 Hex
2. A byte denoting the message length (LGE)
3. A byte denoting the adjustable frequency drive
address (ADR)
A number of data bytes (variable, depending on the type
of message) follows.
A data control byte (BCC) completes the message.
STX LGE ADR DATA BCC
195NA099.10
Figure 7.4
7.4.3 Message Length (LGE)
The message length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
4 data bytes LGE=4+1+1=6 bytes
12 data bytes LGE=12+1+1=14 bytes
Messages containing texts
10
1)
+n bytes
Table 7.4 Length of Messages
1)
The 10 represents the fixed characters, while the “n’” is variable
(depending on the length of the text).
7.4.4
Adjustable Frequency Drive Address
(ADR)
Address format 1-126
Bit 7=1 (address format 1-126 active)
Bit 0-6=adjustable frequency drive address 1-126
Bit 0-6=0 Broadcast
The follower returns the address byte unchanged to the
master in the response message.
7.4.5
Data Control Byte (BCC)
The checksum is calculated as an XOR-function. Before the
first byte in the message is received, the calculated
checksum is 0.
RS-485 Installation and Set... Design Guide
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