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The
DL3000-CMX contains both Modbus Master and
Modbus Slave protocols. When selected for Master mode the DataLink is a
Modbus network "Master". It enables PLCs (or smart devices such as PCs) on
an Allen-Bradley Data Highway Plus network to initiate a Read/Write transfer
of up to 100 registers or 1600 coils to Modbus network slave devices. The
DataLink supports Modbus commands 01, 02, 03, 04, 05, 06, 08, 15, and 16,
and provides an RS232 serial interface to Modbus with optional RS422/RS485
connections available at additional cost.
 DL3000
User's Guide.
DL3000-CMX Application
Notes.
The DL3000-CMX (Master) is a Modbus Master and responds to commands from any
PLC-5 on the DH+ network, translates them to Modbus format and transmits
them to any Modbus slave device on the Modbus network. A Modicon BM85 would
allow PLC-5 commands to be sent to Modicon PLCs on Modbus Plus.
Communications
between the DataLink and Modbus slaves are initiated from a station on DH+.
The DataLink must be the only Master on the Modbus network and does not
require a Modbus address. The DH+ network side of the DataLink unit is an
active station on the DH+ and requires a unique DH+ address. DataLinks will
automatically accept message instructions from PLCs, SLCs, or intelligent
devices on DH+ such as PCs running HMI/GUI software.
The -CMX has
been enhanced to enable the use of PLC-3 commands as well as PLC-5 commands
but the addressing capability is dependent on the PLC type, DH+ message
command set, and PLC programming software used. When the DL3000-CMX receives
a message over DH+, the Destination Data Table Address (DDTA) field is
converted to the corresponding Modbus command, Slave number, and Data
address. Please check the
application note for details on addressing format and limitations.
Operation:
The DataLink
receives a command on its DH+ network channel, converts it to the
appropriate Modbus command, and sends it out on the asynchronous RS232C
Modbus channel to the addressed Modbus slave device. The Modbus slave
response is received by the DataLink Master, converted into the
corresponding DH+ response and directed back to the originating DH+ station.
When the
DataLink receives a PLC-3 / PLC-5 Word Range Read / Write or a PLC-5 Typed
Read / Write message command addressed to its DH+ station number, it
automatically interprets its Destination Data Table Address and translates
it to the appropriate Modbus command and address.
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