Dacta 70909

I've just aquired a Dacta 70909 interface but I can't find much information on the serial protocol (baud, parity, stop, sign on). One site has information on the bizarre 'knocking,
byting' string that initializes the interface (the same as on the RCX) but doesn't expand much on it.
Anyone got any info?
Obviously Lego had nothing to say about it bar it being 'discontinued'.
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