Allen-Bradley Micro830, Manual

Page: 255 / 354

Rockwell Automation Publication 2080-UM002K-EN-E - March 2019 241
Appendix
B
Modbus Mapping for Micro800
Modbus Mapping
All Micro800 controllers (except the Micro810 12-point models) support
Modbus RTU over a serial port through the embedded, non-isolated serial port.
The 2080-SERIALISOL isolated serial port plug-in module also supports
Modbus RTU. Both Modbus RTU master and slave are supported. Although
performance may be affected by the program scan time, the 48-point controllers
can support up to six serial ports (one embedded and five plug-ins), and so
consequently, six separate Modbus networks.
In addition, the Micro850 and Micro870 controller supports Modbus TCP
Client/Server through the Ethernet port.
Endian Configuration
Modbus protocol is big-endian in that the most significant byte of a 16-bit word
is transmitted first. Micro800 is also big-endian, so byte ordering does not have to
be reversed. For Micro800 data types larger than 16-bits (for example, DINT,
LINT, REAL, LREAL), multiple Modbus addresses may be required but the
most significant byte is always first.
Mapping Address Space and supported Data Types
Since Micro800 uses symbolic variable names instead of physical memory
addresses, a mapping from symbolic Variable name to physical Modbus
addressing is supported in Connected Components Workbench software, for
example, InputSensorA is mapped to Modbus address 100001.
By default Micro800 follows the six-digit addressing specified in the latest
Modbus specification. For convenience, conceptually the Modbus address is
mapped with the following address ranges. The Connected Components
Workbench mapping screen follows this convention.