VM600 networking manual MAVM600-NET/E B - 1
Edition 9 - February 2018
APPENDIX B: AMC8 MODBUS REGISTER DEFINITIONS
APPENDIX B: AMC8 MODBUS
REGISTER DEFINITIONS
AMC8 card register definitions for Modbus can be found in the following address map tables:
Table B-1: Read coil or discrete input registers (Modbus function code 01)
Table B-2: Read discrete input registers (Modbus function code 02)
Table B-3: Read input registers (Modbus function code 03)
Table B-4: Read holding registers (Modbus function code 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 software 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 B-1, Table B-2, Table B-3 or Table B-4) to determine
the Address Offset (Aoff). The choice of table depends on the Modbus function code to
be used.
3- Use the following formula to calculate the Modbus starting address (MSA):
MSA = 4096 + Aoff + (256 * Snum) (B.1)
NOTE: To obtain the register number simply add 1 to the calculated MSA value.
Example:
Your AMC8 card is in slot 14 and you want to read the result of the logical combinations of
alarms for the 16 basic functions you defined in the MPS software (they correspond to bits b0
to b15).
To do so, you have to use Modbus function 04 - Read Input Registers.
Looking at Table B-4, you can find that the Aoff = 24.
Finally, using equation (B.1), you obtain the Modbus starting address:
MSA = 4096 + 24 + (256 * 14) = 7704.
Therefore, the register number = 7704 + 1 = 7705.
NOTE: A complete list of Modbus starting addresses as an Excel
®
spreadsheet is
available from Meggitt Sensing Systems on request.
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