You wrote:

>Say I have two interrupt routines.

It's probably better to say that you don't:  one of the tricks I use to save a f
ew
cycles is to do all the interrupt handling "inline",  and check all the possible
interrupt sources on each interrupt.  E.g.:

    Test INTF,  and branch if off
         Handle external interrupt
    Test T0IF,  and branch if off
         Handle TMMR0 overflow
    etc...
    RETFIE

I'd only do CALLs if I had a service routine complicated enough to take up
more page 0 space than I could spare,  or I had lots of spare CPU time,  and
wanted to trade some for a small improvement in readability.  But the
generous use of whitespace in the inline code does almost as well.

>On the RETURN at the end of the RTCC routine, control passes to the service
>routine.  But what if the RB0 flag was checked before the RTCC routine was
>called?  On RETFIE, would the interrupt service routine be called again
>by the uC because a flag was still high??

Yup:  some chips reset their "interrupt pending" status if you peek at it,  but
the PIC requires that you reset it explicitly.  "Just checking" really means
"just checking" in this case:  you have to BCF INTCON,INTF to make it
shut up.  If you don't clear it,  you'll get an unpleasant surprise...

Ran