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