Thanks for the info on S5 floating-point. Quique is correct, except that I think he means "non-bit-hidden" mantissa, rather than "non-normalised". At least, that's what the CP sends. It's sent big-endian (i.e exponent first) BTW.
Next question: What does REPTEL error code 04 mean in 3964 protocol? My ancient manual has only 0A, 0C, 10, 12, 14, 16, 2A, 32, 34, and 46 (all hex). I'm getting 04 with one particular read request. An almost identical read command (different block no) is OK, so does it just mean non-existent block?
Chris