Industrial Gaussmeter IGM11 Operating Instructions
Chapter 9 Serial Interfaces
Page 53 / 106
MAGSYS
magne t
systeme
Version 01/2013
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me GmbH - All Rights Reserved.
9.4.2
Data Encoding
The data telegram is encoded as follows:
•
STX (Start of Text): 1 byte, ASCII character 0x02h (decimal 2)
•
LNG (Telegram length): 1 byte, containing the telegram length as binary
digit
•
ADR (Address byte): 1 byte, containing the slave address and the telegram
type
•
User data: N bytes
•
BCC: 1 byte, checksum (Block Check Character)
9.4.3
Telegram Length
The telegram length is variable. The length of a telegram is specified in the second
byte of the telegram.
The maximum total length of a telegram is 80 bytes load data.
Only the user data (number n), the address byte (ADR) and the backup character are
counted among the telegram length. Thus, the length of a data telegram is two
characters longer than the value of LNG.
A maximum of 80 payload units can be transmitted per telegram.
9.4.4
BCC Generation
Before reception of the first character of a telegram (STX) BCC = 0.
With each reception of a character, BCC
new
becomes BCC
old
XOR "new character".
The result after the last user data is BCC.
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