Parameter Settings To Enable The Protocol; Fc Protocol Message Framing Structure; Content Of A Character (Byte); Telegram Structure - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS485 Installation and Set-...
7.3 Parameter Settings to Enable the
Protocol
To enable the FC protocol for the frequency converter, set
the following parameters.
Parameter
Parameter 8-30 Protocol
Parameter 8-31 Address
Parameter 8-32 Baud Rate
Parameter 8-33 Parity / Stop Bits
Table 7.3 Parameters to Enable the Protocol

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.
Start 0 1 2 3 4
bit
Illustration 7.4 Content of a Character

7.4.2 Telegram Structure

Each telegram has the following structure:
•
Start character (STX) = 02 hex.
•
A byte denoting the telegram length (LGE).
•
A byte denoting the frequency converter address
(ADR).
Several data bytes (variable, depending on the type of
telegram) follow.
A data control byte (BCC) completes the telegram.
STX LGE ADR
Illustration 7.5 Telegram Structure
MG18C702
Design Guide
Setting
FC
1–126
2400–115200
Even parity, 1 stop bit
(default)
5 6 7 Even Stop
Parity bit
DATA BCC
Danfoss A/S © 04/2016 All rights reserved.

7.4.3 Telegram Length (LGE)

The telegram length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
4 data bytes
12 data bytes
Telegrams containing texts
Table 7.4 Length of Telegrams
1) The 10 represents the fixed characters, while the n is variable
(depending on the length of the text).

7.4.4 Frequency Converter Address (ADR)

Address format 1–126
•
Bit 7 = 1 (address format 1–126 active).
•
Bit 0–6 = frequency converter address 1–126.
•
Bit 0–6 = 0 broadcast.
The slave returns the address byte unchanged to the
master in the response telegram.

7.4.5 Data Control Byte (BCC)

The checksum is calculated as an XOR-function. Before the
first byte in the telegram is received, the calculated
checksum is 0.

7.4.6 The Data Field

The structure of data blocks depends on the type of
telegram. There are 3 telegram types, and the type applies
for both control telegrams (master⇒slave) and response
telegrams (slave⇒master).
The 3 types of telegram are:
Process block (PCD)
The PCD is made up of a data block of 4 bytes (2 words)
and contains:
•
Control word and reference value (from master to
slave).
•
Status word and present output frequency (from
slave to master).
STX LGE ADR PCD1
Illustration 7.6 Process Block
Parameter block
The parameter block is used to transfer parameters
between master and slave. The data block is made up of
12 bytes (6 words) and also contains the process block.
LGE = 4+1+1 = 6 bytes
LGE = 12+1+1 = 14 bytes
10 1) +n bytes
PCD2 BCC
83
7 7