Starting up the device - RS 485 Modbus interface
Leuze electronic GmbH + Co. KG
CML 730i
159
14.4 Autosend mode
In normal mode, the master sends a query to the slave and the slave responds.
In autosend mode, the slave constantly sends datablocks to the master; the master activates this by
sending a query to the slave once. In autosend mode, a freely definable datablock (process data –
between 32 and 224 bytes) is transmitted by the CML 700i to the PLC as fast as possible with little
“overhead”.A datablock is transferred only once per measurement.
There are two autosend protocols: the binary protocol and an ASCII protocol.
The binary protocol transfers the process data with little overhead; however, this requires that the short
transfer pauses can be detected to allow the telegrams to be separated.
The ASCII protocol allows a telegram start and end to be found easily using special characters and
provides a better check sum; the gross data volume is, however, roughly twice as large.
To send data in a meaningful way in autosend mode, proceed as follows:
Configure the process data by means of the Modbus command.
Use the control (PLC) to switch the CML 700i to autosend mode (see chapter 14.4.1 "Changeover from
RS 485 Modbus to autosend mode").
14.4.1 Changeover from RS 485 Modbus to autosend mode
Changeover from RS 485 Modbus to autosend binary protocol
Status of process data
object
AA
32 bytes
RO
Representation of the 16 evaluation functions
mapped with the
process data settings
configura
-
tion (see *** 'Process data settings (group 6)' on
Beam-stream object
BD
222 bytes
array
RO
PD beam-stream
Note:
This is the only object for which it is permitted to
specify a length in the read telegram that is
smaller than the object length itself. You can
request between 1 … 222 bytes.
Parameter
Index
(hex.)
Response
Data
type
Access Value
range
Default Explanation
Restrictions/boundary conditions:
Autosend mode is not compatible with the Modbus definition.
Autosend communication is only possible between two participants, i.e., for point-to-point con
-
nection between master (control, PLC) and a slave (CML 700i).
The PLC must be able to process the data transmitted by the CML 700i.
The silent interval has no effect on autosend mode. The silent interval only influences the
response time in RS 485 Modbus mode.
With a silent interval > 0, the response of the CML 700i to a master query is output with a delay
and the RS 485 direction changeover performed (half duplex mode).
To throttle the data output of the CML 700i, select a lower bit rate or use the cascading functions
(see chapter 4.9 "Cascading/triggering").
Message from master (PLC) to slave (CML 700i): (AUTOSEND ON)
HEX: 01 05 00 00 FF 00 8C 3A
Expected answer from slave (CML 700i) to master (PLC): (AUTOSEND ON)
HEX: 01 05 00 00 FF 00 8C 3A