How to Calculate Rc and Choose Diode for ICL 7673 Backup Switching Circuit?

Hello Guys,
I thinking to have a circuit to backup my PIC microcontroller on it even when main power goes out and it switches to the battery. Therefore , i found an IC that i think it suitable for me is ICL 7673. From the attach image i think to use an adapter output with 12V 1A to the Vp.
May I know how to calculate the Rc that use in the image that i post and what diode i should use for the circuit???
Any other way , i can use to make a stand-alone backup circuit???

In the battery application notes, it will define a float voltage and a trickle charge current, The resistor value should be:

R-charge = (5V-Vdiode - Vfloat/I-trickel

As for the diode, the diode has to handle the following current:

I-diode = (5V - Vdiode)/R-triclel (assumes battery is shorted worst case)

The power for the diode/resistor is:

P-diode = I-diode*Vdiode
P-R-charge = I-diode^2 *R-charge

Idiode = (5V – Vdiode)/R-triclel (assumes battery is shorted worst case)

May i know how to found the R-triclel???
IF the battery i use is 6V.
as we know the Vdiode is 0.7V.

Rule of thumb for NiCad is C/10 (or one tenth the rated capacity of the battery, in milli-amp hours [mAh]). It's not good to trickle charge a NiMH battery at that rate for extended periods beyond a full charge. But, I have run indefinite maintenance charge on NiMH batteries at around C/20 with no apparent ill effect. The only draw back is it takes a lot longer to recharge a depleted battery at that rate--but if outages are infrequent, or brief, that should work fine.

So, if the battery is rated with a capacity of 500mAh, then the trickle charge current would be 50ma at C/10 and 25ma at C/20.

BTW: NiMH batteries often don't survive deep discharge. Probably best to not let a NiMH cell drop below 1 volt [it's pretty well depleted at that voltage, anyway].

You can't charge a 6V battery from 5V, what part don't you get?

Yeah, Earl, you're right -- I missed that! But, if the charging voltage IS high enough, then what I said applies.