Which CRC?

Which CRC?

Post by Chri » Thu, 22 Jan 2004 16:03:06



Hi,

Does anyone know what sort of CRC is used for each sector of a floppy disk?
I was thinking it was a standard CCITT 16 bit CRC but my attempts at
generating a correct CRC have failed.  Here's some extracted data from a
disk along with the CRC:

DATA : 0xA1, 0xA1, 0xA1, 0xFE, 0x00, 0x00, 0x01, 0x02
CRC : 0xCA 0x6F

The data is from the address field of the sector.  I'm pretty sure the CRC
includes the first 3 bytes of 0xA1, but I'm not 100% sure.

If anyone has any advice or tips then please let me know.

Thanks in advance,

 
 
 

Which CRC?

Post by glen herrmannsfeld » Fri, 23 Jan 2004 16:20:58



> Does anyone know what sort of CRC is used for each sector of a floppy disk?
> I was thinking it was a standard CCITT 16 bit CRC but my attempts at
> generating a correct CRC have failed.  Here's some extracted data from a
> disk along with the CRC:
> DATA : 0xA1, 0xA1, 0xA1, 0xFE, 0x00, 0x00, 0x01, 0x02
> CRC : 0xCA 0x6F
> The data is from the address field of the sector.  I'm pretty sure the CRC
> includes the first 3 bytes of 0xA1, but I'm not 100% sure.

I believe is it X'1021' which I also believe is the CCITT CRC16.

I believe the A1 are not included, though.  The X'FE' is the
ID address mark, then track address, zero, sector address, zero, CRC.
(One of the zeros is the head address, but I am reading a SS description.)

For data, the Data address mark X'FB', the appropriate number of
data bytes, and the CRC.

I am not so sure, but I believe the bytes are written MSB first, so
the CRC should be done that way, too.   Ethernet is sent LSB first,
so its CRC is calculated that way.

-- glen

 
 
 

Which CRC?

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Quote:> Hi,

> Does anyone know what sort of CRC is used for each sector of a floppy
disk?
> I was thinking it was a standard CCITT 16 bit CRC but my attempts at
> generating a correct CRC have failed.  Here's some extracted data from a
> disk along with the CRC:

> DATA : 0xA1, 0xA1, 0xA1, 0xFE, 0x00, 0x00, 0x01, 0x02
> CRC : 0xCA 0x6F

> The data is from the address field of the sector.  I'm pretty sure the CRC
> includes the first 3 bytes of 0xA1, but I'm not 100% sure.

> If anyone has any advice or tips then please let me know.

> Thanks in advance,

-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.veryComputer.com/ - The #1 Newsgroup Service in the World!
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Which CRC?

Post by Nick Maclar » Wed, 18 Feb 2004 18:25:19




> GET PAYPALED!!!!!!!

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Regards,
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