Change of magnetic polarity on the disk surface induces current in the read/write-head. The signal gets amplified by two NE592 op-amps.


Amplified signals from the NE592's is then fed to a comparator LM311 which outputs low/high according to the magnetic polarity changes. (This is basically the point where Kryoflux samples the signal.)


Output from the LM311 comparator is connected to one input of a 74LS86 2-input XOR gate, and to the other input of the XOR gate via resistor and that pin is also grounded via capacitor so it creates a slight delay on the other input, which in turn makes the 74LS86 output a short high pulse when the magnetic polarity changes.


Output from the LM311 comparator is also connected to the D input of a 74LS74 D-type flip flop.


Output from the 74LS86 XOR gate is then fed to a 9602/74LS123 retriggerable monostable multivibrator, and also the Output Enable -signal from the VIA is connector to this chip to disable it when needed (writing to disk).


The 9602/74LS123 has inputs for external resistor and capacitor for controlling the width of the output pulse when triggered. These two components have been selected to produce approximately 2.5us pulse when triggered.


When the 9602/74LS123 is enabled and triggered by the short pulse from the 74LS86 XOR gate, the 9602/74LS123 _Q output is pulled low for 2.5us. If during that perioid another pulse is seen coming from the 74LS86 XOR gate, the _Q output is held low, for 2.5us from this moment on. If no more pulses are seen from the 74LS86 XOR gate after 2.5us, the 9602/74LS123 _Q output goes back high.


The 9602/74LS123 _Q output is connected to the CLK input of the 74LS74 D-type flip flop where the LM311 comparator is also connected to the D input.


When the _Q output from the 9602/74LS123 brings the CLK input of the 74LS74 high, the Q output of the 74LS74 reflects the current state of the D input.


The Q output from the 74LS74 is then connected again to one input of another 74LS86 XOR gate, and to the other input of the XOR gate via resistor and capacitor to ground to create the delay which makes the XOR gate output only a short high pulse.


The high pulse from the 74LS86 XOR gate is then connected to another 9602/74LS123, which is permanently enabled. The Q output of the 9602/74LS123 then pulses high for approximately 83ns.


The Q output of the 9602/74LS123 is connected to the 74LS193 4-bit binary counters to load the density preset to the main clocking counter and to reset the other counter.