Difference between revisions of "Modbus notes"

Revision as of 23:51, 13 November 2019

• https://en.wikipedia.org/wiki/Modbus

• https://www.embedded-solutions.at/en/freemodbus/freemodbus-examples/

• https://libmodbus.org/ . . . Ubuntu package is 'libmodbus5' and 'libmodbus-dev'

- 2019-11-08 FRI -

When working with FreeModbus, be sure to pay attention to the versions of protocol available, and likely, we only want to enable one of these. See Modbus/include/mbconfig.h. See also Modbus/include/mb.h for instructions on how to initialize and begin to use an instance of FreeModbus stack in given program. Also mention that eMBPoll() routine may be set up as a task in an RTOS, to realize the periodic polling which is part of the stack's runtime manifestation . . .

Looks like also this function to register callbacks for end-user-device-specific Modbus registers will be important:

  eMBErrorCode eMBRegisterCB ( UCHAR ucFunctionCode,
    pxMBFunctionHandler pxHandler
  )

This function signature part of documentation found at https://www.embedded-solutions.at/en/freemodbus/api-documentation/, which gives Doxygen generated API help in an embedded pane in the browser window on which it is visited.

2019-11-12 Tuesday - trying to figure out how pxMBFunctionHandler is defined . . . from http://www.teamfdi.com/uez/docs/mbproto_8h.html:

 Typedefs
 typedef eMBException(* pxMBFunctionHandler )(UCHAR *pucFrame, USHORT *pusLength)

...from this typedef looks like Modbus routines implemented by the end user/end designer must have parameter lists which match "unsigned char pointer, unsigned integer pointer".

^ further references

• https://stackoverflow.com/questions/40239270/freemodbus-embregcoilscb-function-body-example

What do we need to pass to eMBRegisterCB()? . . .

• https://os.mbed.com/users/giryan/code/Modbus/docs/tip/group__modbus.html
C function pointer syntax:
• https://stackoverflow.com/questions/1591361/understanding-typedefs-for-function-pointers-in-c
• https://www.zentut.com/c-tutorial/c-function-pointer/