Applies To:
  • CitectSCADA 3.xx, 4.xx, 5.xx
Summary:
What Modbus function codes does the Citect MODBUS driver support? 

Solution:
The MODBUS driver supports read functions 1, 2, 3, 4 & 20 and write functions 5, 6, 15,16 & 21.

For writes, there is a choice depending upon what addresses you are writing to and how many data blocks are written.  For example, if you are writing to an output register, then the driver will automatically use Fn6 for one (16bit) register or Fn16 for multiple registers (i.e.. writing real numbers or two or more consecutive integers).

See table below for a summary -

 

Citect Addr. Range  Read Fn. Write Fn.
00001 - 09999 1 5 or 15
10001 - 19999 2

-
30001 - 39999 4

-
40001 - 49999 3 6 or 16
E[1-999]:[0-9999] 20 21

Function codes 20 and 21 are only available with Modbus driver version 2.04.07, and later.

See also article Q2930.

Note: Whilst this KB article refers to the MODBUS driver, the comments can also be applied to the MODNET driver.

 
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