There is no choice when conforming to just about any standard. The particular CRC the OP wants to use can be found used as the Header Check Sequence in IEEE 802.6 (Metropolitan Area Network), as an optional shorter FCS in ISO/IEC 13239 (the ubiquitous HDLC protocol and its derivatives), some parts of GSM, and so on. In all of those examples, it is used for very short data blocks.

If the OP is in control of both sides of the CRC generation/checking, then he can do whatever he wants, and seems hell-bent on getting somebody to endorse that particular CRC as suitable to satisfy the only requirement he has given thus far, which from his initial Keil thread is: "i hope to do CRC for 256 byte data".

• Is he trying to use a Maxim part?
  Ivan's not telling us.
• Is he trying to conform to some published comm standard?
  Ivan's not telling us.
• Is he trying to add a CRC to EEPROM or RAM data?
  Ivan's not telling us.
• Is he in control of both sides of the CRC generation/checking?
  Ivan's not telling us.

The only other thing of substance that he's presented is that he "...can only do CRC for 7 bytes.", but never given examples of for us to deduce what is wrong.

That said, Peter has added a nice variation to the typical implementation methods that we see.