Rockwell Automation 20-COMM-H RS485 HVAC Adapter FRN 2.xxx - Manual (Page 41)

Using Modbus RTU 4-9
20-COMM-H RS-485 HVAC Adapter User Manual
Publication 20COMM-UM009D-EN-P
Accessing Drive Parameters There are two methods for accessing drive parameters: the direct access
method and the pointer access method.
Direct Access Method
You can use Function Code 03 to read and Function Codes 06 (single) and
16 (multiple) to write, to directly access the drive parameters (see
Table 4.B on page 4-2 ). This allows direct access of parameters in a single
read or write as opposed to first having to write the “Param# for INx” or
“Param# for OUTx” using the Pointer Access Method.
When a 41000 or higher Modbus address is used, the adapter assumes the
controller is accessing the drive’s parameters directly. The address is
determined by:
16-bit Adapter Mode: Modbus Address = 41000 + (Drive Parameter #)
32-bit Adapter Mode: Modbus Address = 41000 + (Drive Parameter # x 2)
For example, with the adapter in 16-bit mode, Parameter 1 is accessed by
Modbus Address 41000. In the 32-bit mode, Parameter 1 is accessed by
Modbus Address 41002. Any attempts to access a parameter number that
does not exist will return an error.
The 32-bit adapter mode requires a minimum of two registers to read or
write, and is always an even number since two 16-bit registers are read for
each 32-bit data item.
Pointer Access Method
Reading Parameter Values
With a configurable input point, you can read any 16-bit parameter in the
drive. The sequence for reading parameter values is as follows:
1. Set one or more Param# for INx points in the controller to the parameter
number(s) that you want to read. You can set up to eight Param# for INx
points. Refer to
Table 4.I on page 4-10 .
2. Send a message with a Write Single Register (code 06) or Write
Multiple Register (code 16) function. You need to send the Param# for
INx point(s) to the adapter only one time per power cycle because,
when the adapter receives the Param# for INx point(s), it stores them in
its RAM. The adapter then continuously reads the values for the drive
parameters specified in the Param# for INx points.
3. Send a message with a Read Input Registers (code 04) function. The
adapter reads the drive parameter(s) that have been configured in the
Param# for IN point(s) and returns their values in the User INx point(s).
It can return up to eight User INx points. Refer to
Table 4.I on
page 4-10 . You can perform Read Input Registers continuously, if
desired.