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RS-232 communication to a Agilent E3649A, Help

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I'm trying to communicate with a Agilent E3649A DC Power Supply. I have written some code using the CommAPI and so far I am only able to send commands, I cannot receive anything.  When I use the application that comes with the power supply everything is working as it should so that rules out the cable. Can someone look over my test code? I may have missed something...

#include <CommInterface.au3>
#include <MsgBoxConstants.au3>

Local Const $iPort = 1
Local Const $iBaud = 9600
Local Const $iParity = 0
Local Const $iByteSize = 8
Local Const $iStopBits = 2

Local $hFile =_CommAPI_OpenCOMPort($iPort, $iBaud, $iParity, $iByteSize, $iStopBits)

_CommAPI_TransmitString($hFile, "OUTP ON"&@LF) ;Turn output on
Sleep (1000)
_CommAPI_TransmitString($hFile, "VOLT 7.0"&@LF) ;Adjust voltage to 7 volts
Sleep (1000)
_CommAPI_TransmitString($hFile, "VOLT 0.0"&@LF) ;Adjust voltage to 0 volts
Sleep (1000)
_CommAPI_TransmitString($hFile, "OUTP OFF"&@LF) ;Turn output off
Sleep (1000)
_CommAPI_TransmitString($hFile, "*IDN?") ;Identify your-self

Local $sResult =_CommAPI_ReceiveString($hFile, 1, 0);Recieve string


MsgBox($MB_SYSTEMMODAL, "Title", $sResult, 5) 

I know that the commands are being sent properly because I can see the output status change on the display of the power supply and my connected LED lights up and then goes out.

 Also here is a link to the user manual http://cp.literature.agilent.com/litweb/pdf/E3646-90001.pdf

Thank you in advance!

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Not sure why I could not get this to work with CommAPI, but i was able to get this working using >VISA / GPIB library for AutoIt3.  See my attached code. 

#include <Visa.au3>
#include <MsgBoxConstants.au3>

;Open a connection to the instrument.
Local $h_Instr = _viOpen("ASRL1::INSTR") ;"ASRL1::INSTR" is the VISA connection handle for COMM 1 on my PC.
MsgBox($MB_SYSTEMMODAL, "Instrument Handle obtained", "$h_Instr = " & $h_Instr) ;Show the Session Handle.

;Query the instrument.
Local $s_Answer = _viExecCommand($h_Instr, "*IDN?") ;$h_Instr is NOT A STRING now!
MsgBox($MB_SYSTEMMODAL, "GPIB QUERY result", $s_Answer ) ;Show the answer.

_viExecCommand($h_Instr, "OUTP ON") ;Turn output on.
Sleep (1000)
_viExecCommand($h_Instr, "VOLT 7.0") ;Adjust voltage to 7 volts.
Sleep (1000)
_viExecCommand($h_Instr, "VOLT 0.0") ;Adjust voltage to 0 volts.
Sleep (1000)
_viExecCommand($h_Instr, "OUTP OFF") ;Turn output off.
Sleep (1000)
$s_Answer = _viExecCommand($h_Instr, "VOLT?") ;Query the instruments current voltage setting.

; Close the instrument conection.

MsgBox($MB_SYSTEMMODAL, "Title", $s_Answer, 5)
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The OP uses a serial (RS232) communication cable to manage (send commands, receive status and measurements) an Agilent PSU (lab power supply unit) from a PC.

Another commonly used communication is GP-IB (also known as HP-IB).

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use this link for the start: '?do=embed' frameborder='0' data-embedContent>>

Download the "commg.dll" and "CommMG.au3"

I made a change to your code (not to all) and hope that give you a start to begin with ... for communication I used the  CommMG.au3 and commg.dll.  

#include <CommMG.au3>
#include <MsgBoxConstants.au3>

;~  need to add the dll file to work properly
_CommSetDllPath(@ScriptDir & "\commg.dll")

Global $iPort = 1
Global $iBaud = 9600
Global $iByteSize = 8
Global $iParity = 0
Global $iStopBits = 1 ; must be set as 1 for the corect language
Global $iSetFlow = 0
Global $sportSetError = ''
Global $ValRTS = 0
Global $ValDTR = 0

;~ _CommSetPort -- not accepting the "Const" variable
_CommSetPort($iPort, $sportSetError, $iBaud, $iByteSize, $iParity, $iStopBits, $iSetFlow, $ValRTS, $ValDTR)

$iWaitComplete = 1
$sEndChar = @CRLF
$maxlen = 200
$maxtime = 200
;~ _CommSendString("syst:rem" & @CRLF,1)
;~ Sleep(200)
_CommSendString("*cls" & @CRLF, 1)
_CommSendString("*idn?" & @CRLF, 1)
$s_Answer = _CommGetLine($sEndChar, $maxlen, $maxtime)
MsgBox($MB_SYSTEMMODAL, "Title", $s_Answer, 5)

;~ adding new function here// new command line 

_CommClosePort() ;close the communication with com port

This work for me. 

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