Oscillator Frequency of a Ring Oscillator with RC feedback

[jaus tail]

Homework Statement

What is frequency of oscillator in below circuit?

Relevant Equations

f = 1/(2*3.14*R*C)

I'm not sure how will this oscillator work. Assume A is low, so B will be high and the capacitor will charge through B-C- 2Mohm.
Now even D has gone high, so A will be high and B will be low and C will discharge. I'm not sure how the voltage divider rule across RC will take into effect.
I found a similar structure in this link (3rd circuit diagram):
https://www.gadgetronicx.com/square-wave-generator-logic-gates/Ref: Gadgetronix Square Wave Generator Using Logic Gates. But I'm not sure how if the two circuits will work same as position of Capacitor is after 2nd inverter in the diagram in link.

How will the C charge and discharge here?

 

[berkeman]

The circuit from your link has different component values, and lists an equation for the frequency of oscillation. I haven't tried this type of oscillator before, so I need to think a bit more about it to understand how it works...

 

[rude man]

Since these are TTL gates with fairly low input impedances I doubt this circuit would work. I think you'd have to pull pretty hard voltage-wise to get the input to go low, like maybe -50V thru a 50K resistor to produce 1mA fan-in.

Probably intended for CMOS like 74Cxx or rca 4000 series.