
Leuze electronic GmbH + Co. KG
MA 238
i
36
10
Telegram
10.1 Structure of the fieldbus telegram
All operations are performed by control and status bits. Two bytes of control information and two bytes of
status information are available for this purpose. The control bits are a part of the output module and the
status bits are a part of the input bytes. The data starts with the third byte.
If the actual data length is longer than the data length configured in the gateway, only part of the data is
transmitted; the remaining data is lost. In this case, the DL (data loss) bit is set.
The following telegram structure is used between PLC -> fieldbus gateway:
This telegram structure is used between fieldbus gateway -> PLC:
Only the data part with the corresponding frame (e.g., STX, CR & LF) is then transmitted between the
fieldbus gateway and the Leuze end device. The two control bytes are processed by the fieldbus gateway.
The corresponding control and status bits and their meaning are specified in Section 10.2 and Section
10.3.
Further information on the broadcast control bytes and address bits 0 … 4 can be found in chapter
"Modular connection unit MA 3x (S4 switch position C)" on page 72.
10.2 Description of the input bytes (status bytes)
10.2.1 Structure and meaning of the input bytes (status bytes)
Table 10.1:
Structure of the input bytes (status bytes)
Bits of the input byte (status byte) 0
7
6
5
4
3
2
1
0
ND
Address 4 Address 3 Address 2 Address 1 Address 0 Broadcast Command
mode
Control byte 0
CTB
SFB
R-ACK
Control byte 1
Data byte / parameter byte 0
Data
Data byte / parameter byte 1
…
7
6
5
4
3
2
1
0
ND
BO
DL
BLR
DEX
SMA
W-ACK
Status byte 0
DLC7
DLC6
DLC5
DLC4
DLC3
DLC2
DLC1
DLC0
Status byte 1
Data byte / parameter byte 0
Data
Data byte / parameter byte 1
…
7
6
5
4
3
2
1
0
ND
BO
DL
BLR
DEX
SMA
W-ACK
Status byte 0
DLC7
DLC6
DLC5
DLC4
DLC3
DLC2
DLC1
DLC0
Status byte 1
Data byte / parameter byte 0
Data
Data byte / parameter byte 1
…
Bit no.
Designation
Meaning
0
W-ACK
Write-Acknowledge (write confirmation) when using buffer
2
SMA
Service Mode Active
3
DEX
Data exist (data in transmission buffer)