Design Guide | VLT® AutomationDrive FC 360
9.4.2 Telegram Structure
Each telegram has the following structure:
l Start character (STX) = 02 hex.
l A byte denoting the telegram length (LGE).
l A byte denoting the drive address (ADR).
Several data bytes (variable, depending on the type of telegram) follow.
A data control byte (BCC) completes the telegram.
Figure 52: Telegram Structure
9.4.3 Telegram Length (LGE)
The telegram length is the number of data bytes plus the address byte ADR and the data control byte BCC.
Table 32: Length of Telegrams
4 data bytes LGE=4+1+1=6 bytes
12 data bytes LGE=12+1+1=14 bytes
Telegrams containing texts 10
(1)
+n bytes
1) 10 represents the fixed characters, while n is variable (depending on the length of the text).
9.4.4 Drive Address (ADR)
Address format 1–126
l Bit 7 = 1 (address format 1–126 active).
l Bit 0–6 = drive address 1–126.
l Bit 0–6 = 0 broadcast.
The follower returns the address byte unchanged to the master in the response telegram.
9.4.5 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.
9.4.6 The Data Field
The structure of data blocks depends on the type of telegram. There are 3 telegram types, and the type applies to both control telegrams
(master=>follower) and response telegrams (follower=>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:
l Control word and reference value (from master to follower).
l Status word and present output frequency (from follower to master).
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