CHAPTER 4: MODBUS MEMORY MAP MEMORY MAP ORGANIZATION
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 4 - 5
The User Map feature consists of User Map Addresses #1 to #120 at locations 0180h to
01F7h in the Memory Map. These are the setpoints which store the memory map
addresses of the values that are to be accessed. The data registers are read from the User
Map Values #1 to #120 at locations 0100h to 0177h in the Memory Map. Reading the
register at the location of User Map Value #1 returns the value at the address stored in
User Map Address #1, User Map Value #2 the value at User Map Address #2, and so on.
Storing registers is not allowed using the User Map.
The following table shows the register addresses to store in the User Map Addresses #1 to
#6 so that several different data registers can be read in one continuous block from User
Map Value #1 to #6. Reading the User Map Values is done via function code 03h or 04h.
The User Memory Map is only intended to be used to read data in a proficient manner for
the master computer. The communication system should not be configured in a manner
that generates writes to these locations continuously, as these settings are stored in the
EEPROM that has a maximum of 100000 program/erase cycles.
Memory Map Organization
The 750/760 Memory Map describes all the data registers that can be accessed via serial
communications. The Memory Map address range is grouped into several categories as
outlined in the following table. All memory map locations are two byte (16 bit) values. The
remaining pages of this chapter list all locations of the Memory Map. Addresses for all
locations are shown in hexadecimal. Consult the range, step, units, and the data format
(listed after the memory map) to interpret register values.
Many Modbus communications drivers add 40001d to the actual address of the register
addresses. For example, if address 0h was to be read, then 40001d would be the address
required by the Modbus communications driver; similarly, if address 320h (800d) was to be
read, then 40801d would be the address required by the Modbus communications driver.
Table 1: User Map Register Addresses
Data Register
Description
Values to Store in User
Map Addresses
Locations in User Map
Values to Read Data
General Status Store 0200h at 0180h 0100h
Active Condition Store 0210h at 0181h 0101h
Phase A RMS Current Store 0300h at 0182h 0102h
Phase B RMS Current Store 0301h at 0183h 0103h
Phase C RMS Current Store 0302h at 0184h 0104h
Phase CT Primary Store 1100h at 0185h 0105h
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