Alex Sentcha's Blog

If someone wants to visualize processes controlled by the PLC and this PLC is Siemens, then good choice is LibNoDave exchange data library.

What is Libnodave?

Libnodave is a free library for data exchange between a PC and a PLC’s Siemens. The PLCs that can appeal to the S7-200/300/400. Libnodave is written in C + + and can communicate via MPI, PPI and ISO on TCP. Libnodave works on both Windows and Linux and already available in the following programming languages C + +, VB / C #. NET, Delphi and Java.

During development of project based on the Siemens PLC, often needed to simulate interface of the equipment or machine. The purpose of this article is to show how to do it with different languages for PLC engineers, because contents of the source site is sometimes difficult.

Usage of the library:

1. Initialize the socket interface:
  fds.rfd := openSocket(102, '168.143.1.24';
2. Initialize a daveInterface
  dcIn := daveNewInterface(fds, 'IF1',0,daveProtoISOTCP, daveSpeed187k);
3. Initialize the adapter
  if (daveInitAdapter(dcIn) = 0) then ...
4. Initialize a daveConnection
  dc := daveNewConnection(dcIn,2, StrToInt(rack), StrToInt(slot));
5. Connect to a PLC
  if (daveConnectPLC(dc) = 0) then ...
6. Exchange data with that PLC
  daveReadBytes(dc,daveFlags,0,120,30);
  daveWriteBytes(dc,daveFlags,0,120,16,buf);
7. Disconnect from the PLC
  daveDisconnectPLC(dc);
8. Disconnect from the Adapter
  daveDisconnectAdapter(dcIn);

Example:

Reading sequence of the bytes from PLC:

function daveReadBytes(	dc : PdaveConnection;
                      area : longint;
                      DB   : longint;
                     start : longint;
                       len : longint;
                    buffer : pointer) : longint; stdcall; cdecl;

dc     - connection.
aria   - Datablok , Merker, Input, Output.
DB     - when a data block give data block number. Other areas simply give zero.
start  - location of first byte you want to read.
len    - number of bytes you want to read.
buffer - buffer.

Reading 4 variables from PLC. 3 with integers value and one with double value.

procedure Read_4_DW;
var
  data1, data2, data3 : integer;
  data4 : double;
begin:
    response := daveReadBytes(dc,0x83,0,0,16,NIL);
    if res = 0 then
    begin
      data1 := daveGetU32(dc);
      data2 := daveGetU32(dc);
      data3 := daveGetU32(dc);
      data4 := daveGetFloat(dc);
    end;
end;

Writing sequence of the bytes to PLC: 

function daveWriteBytes(dc : PdaveConnection;
                      area : longint;
                        DB : longint;
                     start : longint;
                       len : longint;
                    buffer : pointer) : longint; stdcall; cdecl;
dc     - connection.
aria   - Datablok , Merker, Input, Output.
DB     - when a data block give data block number. Other areas simply give zero.
start  - is the location of the first bait.
len    - number of bytes you want to write.
buffer - buffer.

Writing bits data to PLC:

function daveWriteBits(dc : PdaveConnection;
                     area : longint;
                       DB : longint;
                    start : longint;
                      len : longint;
                   buffer : pointer) : longint; stdcall; cdecl;
dc     - connection.
aria   - Datablok , Merker, Input, Output.
DB     - when a data block give data block number. Other areas simply give zero.
start  - is the location of the first bait.
len    - is the location of the first bit, so if you want to write a m1.0 then start = 8.
buffer - buffer.

Examples with LibNoDave library for:

1. DotNet API
2. Delphi API
3. NetBeans JavaFX
4. Android