AN-960 P.6 _section of Open Fail-Safe describes below about bias resistor.
Please let me know your advice if R=960 ohm at VCC=3V is typo.
I think that R at VCC=3V is 840 ohm .
R1 = R2 = R
VIA – VIB ≥ 200 mV
VIA – VIB = RT = 200 mV
if VCC = 5 V, then R = 1440 Ω
if VCC = 3 V, then R = 960 Ω