Format of HBBCHN parameter block:
Offset	Size	Description	)
 00h	WORD	0006h (length of following data)
 02h	DWORD	-> data buffer in system memory
 06h	WORD	number of bytes to transfer
Note:	this function performs the actual data transfer for a bitBLT set up
	  with HBBR, HBBW, or HCBBW
SeeAlso: #03890,#03892,#03893,#03894