What do the resistors do in this ICL7673 circuit?

[Jerry James]

Hi,

I came across the ICL7673 IC used for a battery backup system but I could not understand exactly what is the role of the R2 and R4 resistors in this circuit (marked with red in the image below).
So my question is: what role does the R2 and R4 resistors have?
When Vp > Vs , P- is high and S- is low and when Vp < Vs, P- is low and S- is high. Since we have the R1 and R3 resistors to bias the base of the PNP transistors, why do we need the R2 and R4 resistors?
If somebody could explain to me (in detail) I would greatly appreciate it.

 

[Jerome Trent]

Below is a functional Diagram of the ICL7673.

Notice the Sbar and Pbar outputs.

It's just the Drain of an FET not connected to anything.  We need to be able to insure that these outputs either go low or go high.  Going low is not a problem, the Source is connected to ground.  Going high is a problem because the Drain does not connect to anything.  In other word, we have no pullup resistor.  The pullup resistor has to be connected externally.  The pullup for Pbar is through R1 and R2.  The pullup for Sbar is through R3 and R4.  So when the FET is off, we can insure there will be a high at the output.