SuperCard Pro Flux Image format (.scp)
I think I understand why it is confusing! This is probably coming from the terminology that I use. When I first described the protection I had to come with a name but it would have been better if I had called it High Frequency Input Signal – No Output Pulse Data Signal.

All explanation below are speculative based on my understanding of the protection but I might be wrong and would be very interested to hear from you when you receive Turrican…

Some basic reminders: in a floppy drive we have a read/write head that is used to perform “saturated recording” (in contrast to a tape recorder doing a “linear recording”). Recording is simple each time you send a signal on the write data channel the flux on the head is reversed. So if you turn on the write gate but do not send a signal you are actually erasing the track (unformatted area). Now on the read channel you read “transitions” (fluxes reversal) from the head with a preamplifier (with Automatic Gain Control) then this analog signal is converted to pulse with the pulse detector (usually LP filter + differentiator + zero crossing detector …). All this is very well explained in AN917 page 3-4 et 14 and AN413
What is of interest to us is that in the read channel electronic the output data pulse are shifted from the analog input and when signal are getting close the output pulse is shifted more (see AN413 page 11). If the input transition are close enough the data detector will end up by “shifting the data pulse outside of normal window” and this will result in NO OUTPUT pulse.

This is quite different from an unformatted area which we could call No Input Flux Transition – Random Output Pulse Data Signal. In that case we do not have any flux reversal under the head and therefore the input circuit works more like a tape recorder. The head pick-up some noise and the input circuitry pushes the ACG to its maximum. This result in the white noise coming from the input head to be turned into random output pulse.
Below is what I think is happening
So what would be interesting when you receive the Turrican game would be the following:
You place a probe either directly after the head or better after the input amplifier but before the integrator and you place a second probe after the pulse detector. The trigger signal should be the index pulse detector. Now you read track 7 of Turrican. I said track 7 because on this track the HFFA-NOFA area is just above the index (a bit before and a bit after) and see if the theory is right!

Messages In This Thread
SuperCard Pro Flux Image format (.scp) - by admin - 11-01-2013, 05:54 PM
RE: SuperCard Pro Flux Image format (.scp) - by DrCoolZic - 12-21-2013, 02:24 AM

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