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Software
890 USE 108 00 August 2001 61
The extended memory Modbus read and write functions are described in the
Modbus Protocol Reference Guide (PI-MBUS-300) as Read/Write General
Reference function codes 20 and 21. The only difference in the E984-251/255 extra
register implementation is the size of the extended memory, which changes the
number of files and the number of registers.
The following table show the E984-251/255 extra register implementation.
Type E984-251 E984-255
State RAM 2K words 2K words
Extended Memory 24K words 24K words
Number of Files 3 files 3 files
Registers in last File 4K words 4K words
Note: Incrementing the pointer beyond 9999 results in an error. However, if the
count is larger, the function block accesses the next file.