ModTest Manual v2.14 - Read File Record (20)

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The Read File Record command reads multiple groups of file registers from the Modbus slave.

Note that file registers are referred to by several different names in the Modbus specifications. They are variously called "file records", "registers" and "references" in the current Modbus specification, and they are called "General References" or "Extended Memory file (6x) references" in the original Modbus specification and the Modbus/TCP specification (with this command being called "Read General Reference").

To add a register group to the request, click the Add button and then enter the group details in the File Register Groups table:

  • File. Enter the number of the file to read from. The file number must be in the range 1 to 65535.

  • Address. Enter the address of the first register to read. File register addresses are also called "record numbers" in the current Modbus specification.

    The current Modbus specification restricts file register addresses to the range 0 to 9999, for no apparent reason. ModTest will accept addresses in the range 0 to 65535.

  • Count. Enter the number of values to be read - for example, if you want to read five 32-bit floating-point values you should enter 5. Note that this count may be different from the number of registers and may also be different from the count that is actually sent in the Modbus message (the settings for 32/64-bit Value Settings are used to convert the count if necessary).

To remove a register group from the request, select the group in the table and click the Delete button.