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Modes
11
Modes
11.1
Functionality of the data exchange
The fieldbus gateway has two different modes that can be selected via the PLC:
• Transparent mode (default setting)
In Transparent mode, all data are sent 1:1 and directly by the serial end device to the
PLC. It is not necessary to use status and control bits here. However, only data bytes
possible for one transmission cycle are transmitted - all others are lost.
The distance between two successive telegrams (without frame) must be more than
20 ms, since there is otherwise no clear separation between them.
ASCII characters are typically expected as data content; under certain circumstances,
the MA therefore detects different control characters as invalid characters in the data
range and truncates them. At 00
because unnecessary bytes are also filled with 00
• Collective mode
In Collective mode, the data of the serial end device is stored temporarily in the fieldbus
gateway by toggling the CTB bit and is not sent to the PLC in blocks until prompted
to do so by the PLC.
On the PLC, a status bit (DEX) then signals that new data is ready for retrieval. This
data is then read out from the fieldbus gateway in blocks (toggle bit).
In order to distinguish between the individual telegrams on the PLC, in Collective mode
the serial frame is sent to the PLC in addition to the data.
The size of the buffer is 1 kByte.
Notice!
In Collective mode, the CTB and SFB bits are needed for communication handling via the
buffer. Telegrams that can also be completely transmitted in one cycle in Collective mode
(including data frame) go directly through. If PLC data is provided and transferred without a
state change of the CTB bit, it goes directly to the RS 232 interface with the set telegram
data length. Incomplete (incl. data frame) or faulty telegrams can cause error messages in
the connected device!
Combination with the Command mode is possible.
Data exchange in blocks must be programmed on the PLC.
11.1.1 Reading slave data in Collective mode (gateway -> PLC)
If the Leuze device transmits data to the fieldbus gateway, the data is stored temporarily in
a buffer. The PLC is signaled via the "DEX" bit that data is ready for retrieval in the memory.
Data is not automatically transmitted.
If no further user data is present in the MA
toggled once as read confirmation to release data transmission for the next read cycle.
52
in the data range, the MA cuts the telegram off
h
h
2xxi
("DEX" bit = "0"), the "R-ACK" bit must be
MA
204i
.
Leuze electronic
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