How pull-up & pull-down works
The left branch is a released pull-up, initially low; the right branch is a released pull-down, initially high. Both use the same R and C. Leakage opposes the desired logic level. R2, C2 and I2 follow R1, C1 and I1. This example uses the common 70% high and 30% low thresholds.
Ideal released inputs with constant opposing leakage. Check the actual device’s VIH/VIL specifications; 70%/30% is an example, not a universal logic standard.
Change the form inputs or click a component value on the schematic. Choose Try in CircuitSim to simulate the configured circuit.