MatrixMonitor™ IOM - Rev 4 - 4/11/2013
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Communications with the Building Management System
In order to communicate with the BMS, Modbus® must be enabled and the communication line
transmission parameters must be set up. These are all set up key pad display user interface. The
set up procedures are accessed for the “Control Setup” submenus. See the section titled “Set
the Control Data” found earlier in this manual for instructions.
The Modbus address must be established and entered. The address can be any number
between 1 and 247. The default address set up in the control is 75.
The transmission parameters must be established and enter. The transmission baud rate must
be selected. MatrixMonitor™ supports baud rates of 9600, 19200, 38400, and 57600. 19200 is
the default rate. Odd, even, and no parity checking can be enabled. Even parity is the default
setting. One start bit and eight data bits are used as required by the Modbus® standard. One
stop bit is used unless no parity checking is specified. In that case two stop bits are used to
conform to the standard.
MatrixMonitor™ only responds to a subset of Modbus® commands. The only commands
enabled are 3(03h), read holding registers, and 6(06h) write holding register. The read holding
registers function does not support reading multiple registers. If the read holding resisters
command (03h) is issued with a request for more than 1 register to read, an exception error will
be returned. MatrixMonitor will ignore broadcast commands with address 0.
MatrixMonitor™ supports the zero-based addressing of the Modbus® specification and
conforms to the 4xxxx mapping convention for the holding registers. Holding register addresses
start with 40001 and are below 49999. Holding register 40001 is addressed as 0000 in a
Modbus® message. All holding registers can be read with the Modbus® read holding registers
command (03h) from the master. Only selected registers can be written to by the master using
the write holding register command (06h).
A complete list of holding registers available to the
BMS is in the appendix of this document.
In general all of the data available on the data display
screens is available through a Modbus® read registers (03h) command. Almost all of the data
that can be entered through the set up screens on the keypad display unit and be written with
the write register command (06h). The exception to this is the communication set up data.
These parameters must be entered before communication can begin and are not available for
change with Modbus® commands.
