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This feedback loop looks similar to a LFSR, however there are no registers present. It looks to be some kind of oscillator.

There seem to be three inputs to this component, IXP10 (pin 111), STBE (pin 237) and STBF (pin 239). There is also a tap, CGMC (pin 240).

The loop in question The loop in context

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  • \$\begingroup\$ Why not use a simulator and get the operation from that? \$\endgroup\$ – Andy aka Dec 10 '18 at 9:36
  • \$\begingroup\$ I've done that. On a falling edge on 40240/43 (The three input NOR) a short pulse (High) outputs on CGMC. I leave to others to find out exactly what that means. I don't have the knowledge in how the inputs are generated to find it out. @tofro 's answer below might help. \$\endgroup\$ – UncleBod Dec 10 '18 at 13:11
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This is definitely not an oscillator. The output signal of the circuit is in fact CGMC, which is used to clear the register G after it has been used by multiplication or division operations as an auxiliary register.

STBE and STBF are the strobe signals for Erasable and Fixed memory.

The whole circuit looks to me like a timing delay generator that is triggered by the memory strobe signals and generates a clear pulse for the G register with a defined length and delay set by the NOR gates' propagation delays.

Source: This text

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