VM600 networking manual MAVM600-NET/E A - 1
Edition 9 - February 2018
APPENDIX A: MPC4 MODBUS REGISTER DEFINITIONS
APPENDIX A: MPC4 MODBUS
REGISTER DEFINITIONS
MPC4 card register definitions for Modbus can be found in the following address map tables:
Table A-1: Read coil or discrete input registers (Modbus function codes 01 and 02)
Table A-2: Read input or holding registers (Modbus function codes 03 and 04).
These tables include a column (CPUM <71) to indicate if the Modbus register is available in
a particular version of CPUM firmware. In general, most Modbus registers are available but
CPUM cards running firmware version 071 or later have access to all Modbus registers.
These tables include the information required to calculate the Modbus starting addresses
(MSAs). These addresses must be known to access the required registers and can be
determined using the following technique:
1- Decide in which slot the card will be inserted (Snum).
2- Use the appropriate table (Table A-1 or Table A-2) to determine the Address Offset
(Aoff). The choice of table depends on the Modbus function code to be used.
3- Use the formula given in the Modbus starting address (MSA) column of the table to
calculate the MSA.
NOTE: To obtain the register number simply add 1 to the calculated MSA value.
Example:
Your MPC4 card is in slot 5 and you want to read the result of the logical combinations of
alarms for the 8 basic functions you defined in the MPS software (they correspond to bits b0
to b7).
To do so, you have to use Modbus function 04 - Read Input Registers.
Looking at Table A-2, you can find that the Aoff = 1144.
Finally, using the equation given in the table, you obtain the Modbus starting address:
MSA = ( ( slot - 3 ) * 3 ) + Aoff = ( 5 - 3 ) * 3 ) + 1144 = 1150.
Therefore, the register number = 1150 + 1 = 1151.
NOTE: A complete list of Modbus starting addresses as an Excel
®
spreadsheet is
available from Meggitt Sensing Systems on request.
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