There are a couple of things that can be more the less identified:
- the nand gate with resistor and capacitor form an oscillator .. see picture below ..
- voltage at pin 9 will be 1/2 of pin 20, but how high is the supply voltage one can only guess - maybe 5V ..
- 12kΩ and 150pF could be RC components used by the internal oscillator ..
- there are 8 outputs - most likely this is 8-bit converter ..
It is possible that each time the WR input is pulled-down by the output of the 4093 Schmitt triger gate the input analog signal is converted and the outputs are then written with the result of the A/D conversion ..
And that's about it .. the rest is just guessing work ..
Hey,
Can't say I'm 100% sure about this but I think the NAND gate acts as an embedded oscillator,
the voltage at pin9 is ½pin20 and input voltage should be a standard value which would be 5 or 12V though sometimes 15V is also a standard input for an IC, try simulating and see what happens.