INT 48 - TI Professional PC - CALCULATE CRC

	AH = 06h
	ES:BX -> memory block for which to calculate CRC
	BP = size of block in bytes
Return: DX = CRC for block
	ZF set if DX = 0000h
Note:	if the CRC of a memory block is appended to the block, then the CRC
	  of the block plus CRC should equal 0000h
SeeAlso: AH=00h,AH=01h,AH=02h,AH=03h,AH=04h,AH=06h,AH=08h,AH=0Ah,AH=0Bh