DS2488 request a strong pull up during power up (i.e. 5V come up quickly). The typical rising time <300us.
Internally the oscillator runs at 33.3us periods. Upon power up here is what occurs:
1. POR - The device starts in the POR state on power-up through VL or IOA parasite power. Communication is ignored during the POR tOSCWUP time as the device initializes. The warmup delay only occurs on power-up. The spec shows this as tOSCWUP with a typical of 1.5ms and a max of 5ms. However, if already warmed up then this can be close to one state transition or 33.3us.
2. For the IOA > VCMP state (i.e. high voltage detect), there is a small digital deglitch circuit. VCMP has to be high for 4*33.3us samples before is it detected, and low for 4*33us samples before it is undetected. It has no programmability, except for trimming the osc slow. So this check takes 8 x 33.3us = 266.4us with our trim settings before CD/PIOC would be pulled low for slow slew.
When we combine steps 1 and 2 then we know it 266.4 + 33.3us = 299.7us<300us.