7–16
PQM POWER QUALITY METER – INSTRUCTION MANUAL
MODBUS MEMORY MAP
CHAPTER 7: MODBUS COMMUNICATIONS
7.3
Modbus Memory Map
7.3.1
Memory Map
Information
The data stored in the PQM is grouped as Setpoints and Actual Values. Setpoints can be
read and written by a master computer. Actual Values can be read only. All Setpoints and
Actual Values are stored as two byte values. That is, each register address is the address of
a two byte value. Addresses are listed in hexadecimal. Data values (Setpoint ranges,
increments, factory values) are in decimal.
7.3.2
User-definable
Memory Map
The PQM contains a User Definable area in the memory map. This area allows remapping
of the addresses of all Actual Values and Setpoints registers. The User Definable area has
two sections:
1.
A Register Index area (memory map addresses 0180H-01F7H) that contains 120
Actual Values or Setpoints register addresses.
2.
A Register area (memory map addresses 0100H-017FH) that contains the data at the
addresses in the Register Index.
Register data that is separated in the rest of the memory map may be remapped to
adjacent register addresses in the User Definable Registers area. This is accomplished by
writing to register addresses in the User Definable Register Index area. This allows for
improved throughput of data and can eliminate the need for multiple read command
sequences.
For example, if the values of Phase A Current (register address 0220H) and Phase A Power
Factor (register address 02DDH) are required to be read from a PQM, their addresses may
be remapped as follows:
1.
Write 0220H to address 0180H (User Definable Register Index 0000) using function
code 06 or 16.
2.
Write 02DDH to address 0181H (User Definable Register Index 0001) using function
code 06 or 16.
A read (function code 03 or 04) of registers 0100H (User Definable Register 0000) and
0101H (User Definable Register 0001) will return the Phase A Current and Phase A Power
Factor.
