So far I had only thought of one interrupt to use for my project, and I figured I would set it at low priority since there seemed to be no reason to use high-priority when using only one interrupt. Then if later on I discovered that another interrupt was needed, I supposed it might be a higher priority and would then use high priority for it. So, yes, I may need only one interrupt and didn't know of a reason to set it at high priority.

Interestingly, I think, my PICBASIC PRO manual states in section 9.3 "In any case, you must restore these registers at the end of your assembler interrupt handler. If the 14-bit core PIC MCU has 2K or less of code space, or it is an PIC18 device, the registers are not saved. Your interrupt handler must save and restore any used registers." However, the on-line PICBASIC PRO manual doesn't have such a statement and I hadn't read that section of the on-line manual until this morning. I don't see anything about high or low priority interrupts in the manuals. I suppose MEL can't be expected to put "everything about everything" in their manual but interrupts are a particularly important topic, I think.

I wasn't planning on using the DT_INTS, figuring that my project is so simple that DT_INTS wouldn't be required. In retrospect, I probably should use DT_INTS but I need to get my code running right away (yesterday, of course) and our Procurement Department takes a couple of weeks or more to purchase anything and I don't want to spend my own $. BTW, I am a firm believer in macros but have always made my own macros.

So, in conclusion:
1. Use the high priority interrupts if possible.
2. For high priority interrupts, use RETFIE FAST ; return from interrupt, restore shadows.
3. If I have to use low-priority interrupts, I have to save the registers and they can be saved anywhere, using MOVFF to restore them. Also have to use "RCON.7 = 1 ; enable interrupt priorities. And clear the corresponding priority bit for the interrupt you're using ...IPR1.5 = 0 ; set RCIF to low priority. And always remember to use GIEL INTCON.6 instead of GIEH INTCON.7"

This all seems overly complex with all sorts of special rules, but I guess it comes with the high-capability of the beast. I come from the days of (even before) the DEC PDP8 and PDP9, and am overwhelmed with this complexity.

I just now discovered a very useful thread from 2006 with Darrel's info about interrupts. Not sure why I didn't see this earlier: http://www.picbasic.co.uk/forum/showthread.php?t=3251

Now to get back to my home "industrial controller" project with the dsPIC33F and the MPLAB GNU C compiler. That's beginning to seem simpler than using PICBASIC PRO. ;-)

Thanks again for all the very useful info!