Rs485: Fc Protocol Telegram Structure - Danfoss VLT AutomationDrive FC 361 Series Design Manual

Appendix

11.5 RS485: FC Protocol Telegram Structure

11.5.1 Content of a Character (Byte)
Each character transferred begins with a start bit. Then 8
data bits are transferred, each 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 1 characters in the 8 data bits and the parity bit
in total. A stop bit completes a character, thus consisting
of 11 bits in all.
Start 0 1 2 3 4
bit
Illustration 11.5 Character (Byte)
11.5.2 Telegram Structure
Each telegram has the following structure:
•
Start character (STX)=02 hex.
•
A byte denoting the telegram length (LGE).
•
A byte denoting the drive address (ADR).
A number of data bytes (variable, depending on the type
of telegram) follows.
A data control byte (BCC) completes the telegram.
STX LGE ADR
Illustration 11.6 Telegram Structure
11.5.3 Telegram Length (LGE)
The telegram length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
•
The length of telegrams with 4 data bytes is
LGE=4+1+1=6 bytes.
•
The length of telegrams with 12 data bytes is
LGE=12+1+1=14 bytes.
•
The length of telegrams containing texts is 10
bytes.
1) The 10 represents the fixed characters, while the n is
variable (depending on the length of the text).
MG06K102
Design Guide
5 6 7 Even Stop
Parity bit
DATA BCC
1)
+n
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11.5.4 Drive Address (ADR)
Two different address formats are used.
The address range of the drive is either 1–31 or 1–126.
•
Address format 1–31
- Bit 7=0 (address format 1–31 active).
-
Bit 6 is not used.
- Bit 5=1: Broadcast, address bits (0–4) are
not used.
- Bit 5=0: No broadcast.
-
Bit 0–4=drive address 1–31.
•
Address format 1–126
- Bit 7=1 (address format 1–126 active).
-
Bit 0–6=drive address 1–126.
- Bit 0–6=0 broadcast.
The slave returns the address byte unchanged to the
master in the response telegram.
11.5.5 Data Control Byte (BCC)
The checksum is calculated as an XOR-function. Before the
st
1 byte in the telegram is received, the calculated
checksum is 0.
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