Alastair,
Seems like you are the resident expert on Hikvision here.
I'm trying to help out a friend that bricked a DS-9016HFI-ST, and have only spent about 20 minutes with it so far, I tried to connect to the console (RS-232) port on the back to watch what was going on and saw nothing, the only thing that is not clear to me is if I need a null modem cable or a straight thru serial cable.
Scott
Then use Analysis | Checksums | Checksum-16 to calculate the new value.