COMMUNICATIONS GUIDE
MODBUS MEMORY MAP
469 MOTOR MANAGEMENT RELAY – COMMUNICATIONS GUIDE
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Modbus Memory Map
Memory Map Information
The data stored in the 469 is grouped as setpoints and actual values. Setpoints can be read
and written by a master computer. Actual Values are 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.
NOTE
Note
Many Modbus communications drivers add 40001d to the actual address of the register
addresses. For example: if address 0h was to be read, 40001d would be the address
required by the Modbus communications driver; if address 320h (800d) was to be read,
40801d would be the address required by the Modbus communications driver.
User-Definable Memory Map Area
The 469 has a powerful feature, called the User Definable Memory Map, which allows a
computer to read up to 125 non-consecutive data registers (setpoints or actual values) by
using one Modbus packet. It is often necessary for a master computer to continuously poll
various values in each of the connected slave relays. If these values are scattered
throughout the memory map, reading them would require numerous transmissions and
would burden the communication link. The User Definable Memory Map can be
programmed to join any memory map address to one in the block of consecutive User Map
locations, so that they can be accessed by reading these consecutive locations.
The User Definable area has two sections:
1.
User-Definable Addresses 1 to 125 (memory map registers 0180h to 01FCh) that
contain 125 actual values or setpoints register addresses.
2.
User-Definable Values 1 to 125 (memory map registers 0100h to 017Ch) that contains
the data in the corresponding user-definable addresses.
Register data that is separated in the rest of the memory map may be remapped to
adjacent register addresses in the values area. This is accomplished by writing to register
addresses in the user-definable address area. This improves data throughput and can
eliminate the need for multiple read command sequences.
For example, if the values of Average Phase Current (register address 0306h) and Hottest
Stator RTD Temperature (register address 0320h) are required to be read from an 469, their
addresses may be remapped as follows:
1.
Write 0306h to address 0180h (User Definable Address #1) using function code 06 or
16.
2.
Write 0307h to address 0181h (User Definable Address #2) using function code 06 or
16 (Average Phase Current is a double register number).
3.
Write 0320h to address 0182h (User Definable Address #3) using function code 06 or
16.
A read (function code 03 or 04) of registers 0100h (User Definable Address #1) and 0101h
(User Definable Address #2) will return the Phase A Current and register 0102h (User
Definable Address #3) will return Hottest Stator RTD Temperature.
