Concatenate binary number

[Xray45]

Hi everyone,

Does anyone know how to concatenate a binary number to another binary number? I would like to know this for crc calculation.

Manny thanks,

Ray

[RGV250]

Can you actually concatenate binary, I thought it was only text or strings??

Bob

[John Drew]

I agree with Bob, what exactly are you trying to do Ray? Maybe you want to And or Or or Xor.
John

[Xray45]

I am trying to write a CRC-7 routine for writing to a SD-card. I read online that the message as a whole forms a big binary number on which you perform Xor.

[John Drew]

Is the message a row of ASCII ones and zeros and you need to put that into a dword?
John

[top204]

The CRC values are only really required with certain commands sent to the SD card and the values required can be pre-calculated as constants, then used in a simple comparison.

I did a bit of research and I have just created the procedure below that "should" perform a CRC7 calculation. It is untested, but should give you some pointers for the code:

Code Select Expand

'
' Create a global variable for the CRC7_Update procedure to update
'
    Dim Global_bCRC As Byte             ' Holds the CRC value that is updated with bytes read

'-------------------------------------------------------------------------------
' Update a CRC value
' Input     : Global variable Global_bCRC holds the CRC value to update
'           : pData holds the data to add to the Global_bCRC variable
' Output    : Global Variable Global_bCRC holds the updated CRC value
' Notes     : None
'
Proc CRC7_Update(pData As Byte)
    Dim bTemp As Byte
   
    pData = pData ^ Global_bCRC
    Global_bCRC = pData >> 4
    bTemp = (Global_bCRC ^ (Global_bCRC >> 3))
    pData = pData ^ bTemp
    bTemp = pData << 1
    Global_bCRC = bTemp ^ (pData << 4)
EndProc

'---------------------------------------------------------------------------------
Main:

    Global_bCRC = 0
    CRC7_Update(10)
    CRC7_Update(20)


The global variable "Global_bCRC" will be updated by the CRC7_Update procedure with the data sent to it.

If memory serves, SD cards also use a CRC16 calculation for some commands, but, again, these can be pre-calculated because the values returned from the commands are known.

[Xray45]

Thanks very much for the reply, I think i've got enough to go on. Did a bit more reading and indeed they can be pre-calculculated. Still would like to be familiar with the way to calculate them, so i'm going to play around a bit with the example of Top204.