ABB A43 User Manual page 183

Communication with M-Bus
The C-Field (control field) contains information about the direction of the data
The C-Field
flow and error handling. Besides labeling the functions and the actions caused by
them, the control field specifies the direction of data flow and is responsible for
various parts of the communication to and from the meter.
The following table shows the coding of the C-Field:
Bit No.
To meter
From meter
The primary message bit (PRM) is used to specify the direction of the data
flow.It is set to 1 when a telegram is sent from a master to the meter and to 0 in
the other direction.
The frame count bit valid (FCV ) is set to 1 by the master to indicate that the frame
count bit (FCB) is used. When the FCV is set to 0, the meter ignores the FCB.
The FCB is used to indicate successful transmission procedures. A master shall
toggle the bit after a successful reception of a reply from the meter. If the
expected reply is missing, or the reception of it is faulty, the master resends the
same tele-gram with the same FCB. The meter answers, to a REQ_UD2-request
with tog-gled FCB and a set FCV, with a RSP_UD containing the next telegram
of a multi-telegram answer. If the FCB is not toggled it will repeat the last
telegram. The actual values will be updated in a repeated telegram.
On receipt of a SND_NKE the meter clears the FCB. The meter uses the same
FCB for primary addressing, secondary addressing and point-to-point
communi-cation.
The bits 0 to 3 (F0, F1, F2 and F3) of the control field are the function code of
the message. The following table shows the function codes:
Comand
SND_NKE
SND_UD
REQ_UD2
RSP_UD
2CMC48001M0201
Revision: C
7 6 5 4
0 PRM FCB FCV
0 PRM 0 0
C-Field C-Field Telegram
(binary) (hex)
0100 0000 40 Short frame
01F1 0011 53/73 Long frame
01F1 1011 5b Short frame
0000 1000 08 Long frame
183
3 2 1 0
F3 F2 F1 F0
F3 F2 F1 F0
Description
Initialization of meter
Send user data to meter
Request for class 2 data
Data transfer form meter to
master after request.
A43/A44
User Manual