Applies To:
  • CitectSCADA 5.xx

I want to be able to send/receive smaller data link layer frames. 

For DNP devices that have small data link layer frames, then for the same size application layer buffer, more data link layer frames will be produced.  The library that the DNP driver utilises was previously assuming that the DNP device would have a maximum data link layer frame size of 292 bytes, and an application layer fragment maximum size of 2048 bytes.  This combination would result in a maximum of 9 frames per fragment.  The library has been modified such that it will allow up to 64 frames per fragment, however the main practical restriction introduced is that the resulting application layer data from the combined frames will not overflow the application layer buffer.  Now DNP devices with maximum data link layer frame size of less than 292 bytes are also supported.

Similarly, the INI parameter "[DNP] DataLinkFrameSize" allows the specification of the Max data link layer transmit frame size. The default value is 292 bytes. The parameter value is upper limited to 292 bytes, and lower limited to 28 bytes.

This INI parameter is available in version 1.04.00 of the driver (or later).