Serial com-port communication with autoIt

This weekend I found out how to read from / write to a com port with autoIt code. I created a file with some functions that read/write single characters or lines. To communicate with a com port, I use the CreateFile function from Kernel32.dll. This is my first script where I call dll functions from within autoIt, so perhaps the code can be cleaned up some more. 

First, we’ll create a handle to the CreateFile function to open the com port (com2 in this example):

#include <WinAPI.au3>

;init DLL function, we need handle to call the function
$h = DllCall("Kernel32.dll", "hwnd", "CreateFile", "str", "\\.\COM2", "int", BitOR($GENERIC_READ,$GENERIC_WRITE), "int", 0, "ptr", 0, "int", $OPEN_EXISTING, "int", $FILE_ATTRIBUTE_NORMAL, "int", 0)
$handle=$h[0]

To write a single character, I created the writeChar function:

;write a single char
func writeChar($handle,$c)
    $stString       = DLLStructCreate("char str")
    $lpNumberOfBytesWritten = 0
    DllStructSetData($stString, 1, $c)
    $res = _WinAPI_WriteFile($handle, DllStructGetPtr($stString, "str"), 1,                                      $lpNumberOfBytesWritten)
    if ($res<>true) then
       ConsoleWrite ( _WinAPI_GetLastErrorMessage() & @LF)
    EndIf
EndFunc

A struct that contains a single character is created first. On the third line the character is passed to this struct. Then the _WinAPI_WriteFile function is called with the struct as argument. If everything is ok, then the character is written to the com port! The other functions work in a similar manner, and can be found in the attachment. 

This code is very usefull to communicate with microcontrollers, like a PIC uC for example. I was already able to communicate with Matlab (see my other article) which is very usefull for plotting sensor values. The autoIt communication is usefull for remote controlling Windows applications. A simple demo app to illustrate this:

autoIt Code:

#include "pcSide2.au3"
While 1
     $data = readLineBlock($handle)
     ConsoleWrite(">" & $data)
     switch $data
          case "L" & @LF
               send("{MEDIA_PREV}")
          case "R" & @LF
               send("{MEDIA_NEXT}")
          case "U" & @LF
               send("{VOLUME_UP}")
          case "D" & @LF
               send("{VOLUME_DOWN}")
          case "C" & @LF
               send("{MEDIA_PLAY_PAUSE}")
     EndSwitch
Wend

PIC code:

while (1) {
     if (!(BUTTON_CENTER)) {	//BUTTON_CENTER pressed
          fprintf (_H_USART, "C\n");
          while(!(BUTTON_CENTER));	//wait till button released
     }
     if (!(BUTTON_UP)) {	//BUTTON_UP pressed
          fprintf (_H_USART, "U\n");
          while(!(BUTTON_UP));	//wait till button released
     }
     ... 
}

So the autoIt code just waits for characters to be sent. If one of the characters U,D,L,R or C is sent (the characters come from Up,Down,Left,Right,Center in case you’re wondering), autoIt will emulate a keypress of one of the Media functions.

The PIC code  will send one of the characters when a certain button is pressed. So we are able to remote controll our media player (e.g. Windows Media Player) with our PIC uC!

Attachments:

[ com functions for autoIt ] 2kB 
[ demo Application (autoIt code) ] 0kB