Re: Questions on Disk ][ error checking

[mwillegal <mike@willegal.net>]

Actually, the check is kind of an odd 8 bit check, since it is done on
the nibblized sector data that has already been through the decode
process.  Valid values are from 0 to 0x3f.  The upper two bits
are part of the check, but should always be zero.   If you look at the
data before packing it into bytes (denibblizing) and you see
either of the high bits set, you know that that particular byte had an
issue.