Solved

Converting C code into VB.Net 2008

Posted on 2009-05-20
6
320 Views
Last Modified: 2012-05-07
Hello,

following is the code in C used in Modbus CRC calculation. Can someone convert this into VB.Net code since I am not good at C?

Regards,
MI
void ModbusRTU_CalculateCrc(void)
{
	BYTE ucCount = RESET,ucNoOfBits = RESET;
	WORD iCrc;
	
	iCrc = 0xFFFF ^ (*g_pucCRC_Buffer);
	
	for(ucCount = 1; ucCount <= g_ucCRCBufferCount ; ucCount++)
	{
		for(ucNoOfBits = 0; ucNoOfBits <= 7; ucNoOfBits++)
		{
			if((iCrc & 0x01) == 0X01)
			{
				iCrc >>= 1;
	        	iCrc = iCrc^0xA001;
			}	
			else
			{
				iCrc >>= 1;
            }
	 	}
		
		if(ucCount != g_ucCRCBufferCount)
		{
			iCrc = iCrc^(*(++g_pucCRC_Buffer));
		}
		else
		{
		}
	 }
	 
	//Extract lower byte crc.
	g_ucCRCLowByte = iCrc&0x00FF;
	//Extract higher byte of crc.
	g_ucCRCHighByte = ((iCrc>>8)&0x00FF);
	//End of function ModbusRTU_CalculateCrc()
}

Open in new window

0
Comment
Question by:vj_mi
  • 3
  • 2
6 Comments
 
LVL 15

Expert Comment

by:oobayly
ID: 24435665
Rather than reinventing the wheel, I did a quick google:
http://modbus.control.com/thread/1026164935

It appears to be VB6 code, but it's quite easy to translate into VB.Net
0
 
LVL 15

Expert Comment

by:oobayly
ID: 24435941
Saying that, I'm a masochist. Best test that it works properly though!
A couple of things: The C code uses DWORD, which is an unsigned 16bit integer. As VB.Net isn't too keen on UInt16, I've used a 32bit integer instead.
I've used a cross between the C code and the VB code in the link. I didn't like the C loop, and I didn't like the VB bitshifting (mainly because VB6 doesn't have a bitshift operator)
Private Shared Function ModbusCRC(ByVal buff As Byte()) As Integer
    Dim crc As Integer = &Hff
    For i As Integer = 0 To buff.Length - 1
        crc = crc Xor buff(i)
        For j As Integer = 0 To 7
            If (crc And &H1) = &H1 Then
                crc >>= 1
                crc = crc And &Ha001
            Else
                crc >>= 1
            End If
        Next
    Next
    
    ' Lower & Upper bytes (if you need them)
    Dim lower As Byte = CByte(crc And &Hff)
    Dim upper As Byte = CByte((crc >> 8) And &Hff00)
    
    Return crc
End Function

Open in new window

0
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 500 total points
ID: 24437096
Translated from your code (mind the notes in the comments)
Public Sub ModbusRTU_CalculateCrc()
    'Assumes you have the next line declared globally elsewhere
    'Dim g_pucCRC_Buffer, g_ucCRCBufferCount, g_ucCRCLowByte, g_ucCRCHighByte As Integer
 
    'Assumes RESET equals 0
    Dim ucCount As Integer = 0, ucNoOfBits As Integer = 0
    Dim iCrc As Integer
 
    iCrc = &HFFFF Xor g_pucCRC_Buffer
 
    For ucCount = 1 To g_ucCRCBufferCount
        For ucNoOfBits = 0 To 7
            If iCrc And &H1 = &H1 Then
                iCrc >>= 1
                iCrc = iCrc Xor &HA001
            Else
                iCrc >>= 1
            End If
        Next
 
        If ucCount <> g_ucCRCBufferCount Then
            g_pucCRC_Buffer += 1
            iCrc = iCrc Xor g_pucCRC_Buffer
        End If
    Next
 
    g_ucCRCLowByte = iCrc And &HFF
    g_ucCRCHighByte = (iCrc >> 8) And &HFF
 
End Sub

Open in new window

0
Netscaler Common Configuration How To guides

If you use NetScaler you will want to see these guides. The NetScaler How To Guides show administrators how to get NetScaler up and configured by providing instructions for common scenarios and some not so common ones.

 
LVL 15

Expert Comment

by:oobayly
ID: 24439308
Just noticed my code calculates upper incorrectly, originally I had done the bitshift after the bitwise and.
Also, ignore my comments on DWORD, I was reading it as WORD by mistake.
Where was my mind when I posted the answer? <sigh>
Dim upper As Byte = CByte((crc >> 8) And &Hff)

Open in new window

0
 

Author Comment

by:vj_mi
ID: 24452937
Hi friends,

I am yet to test the above code snippets since we got bounced by the data that we send to serial port. Unless that code is fixed, I cannot run the above code snipper. Please bear with me for a day or two. Meantime, I will post the serial port issue as a new thread.

Regards,
MI
0
 

Author Comment

by:vj_mi
ID: 24503008
oobayly:
The code you have mentioned (along with the rectification you asked for returns both lower and upper bytes as 0.

kaufmed:
I had to modify the code slightly for it to work...

Regards,
MI
0

Featured Post

DevOps Toolchain Recommendations

Read this Gartner Research Note and discover how your IT organization can automate and optimize DevOps processes using a toolchain architecture.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Exit the loop 4 42
VB.NET 2008 Publish Error 2 27
vb.net class 3 12
Create a datatable in vb.net dynamically 1 14
Introduction When many people think of the WebBrowser (http://msdn.microsoft.com/en-us/library/2te2y1x6%28v=VS.85%29.aspx) control, they immediately think of a control which allows the viewing and navigation of web pages. While this is true, it's a…
1.0 - Introduction Converting Visual Basic 6.0 (VB6) to Visual Basic 2008+ (VB.NET). If ever there was a subject full of murkiness and bad decisions, it is this one!   The first problem seems to be that people considering this task of converting…
Along with being a a promotional video for my three-day Annielytics Dashboard Seminor, this Micro Tutorial is an intro to Google Analytics API data.
This video shows how to use Hyena, from SystemTools Software, to bulk import 100 user accounts from an external text file. View in 1080p for best video quality.

770 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question