Telegram Format; Field Description - ABB A43 User Manual

Communication with M-Bus
Command
Read request voltage harmonics

10.2.1 Telegram Format

M-Bus uses 3 different telegram formats. The formats are identified by the start
General
character.
Single Character
E5H
The Single Character format consists of a single character and is used to ac-
knowledge received telegrams.
The Short Frame format is identified by its start character (10h) and consists of
five characters. Besides the C- and A-fields it includes the check sum and the
stop character 16h.
The Long Frame format is identified by its start character (68h) and consists of a
variable number of characters. After the start character the L -field is transmitted
twice, then the start character once again followed by the C-, A- and CI-fields.
The user data (0 - 252 bytes) is transmitted after the CI-field followed by
the check sum and the stop character (16h).

10.2.1.1 Field description

All fields in the telegram have a length of 1byte (8 bits).
General
The L-Field (length field) gives the size of the user data (in bytes) plus 3 (for the
The L-Field
C-, A- and CI-Fields). It is transmitted twice in the telegrams using the long frame
format.
2CMC48001M0201
Revision: C
Short Frame
Start (10h)
C-Field
A-Field
Check Sum
Stop (16h)
181
Long Frame
Start (68h)
L-Field
L-Field
Start (68h)
C-Field
A-Field
CI-Field
User Data (0-252 Bytes)
Check Sum
Stop (16h
A43/A44
User Manual