If not, how or when does T1VAL get set?
No the T1VAL MMR will keep the actual count. Writing to T1LD MMR while Timer 1 is running updates T1VAL MMR. You can write a new value to T1LD MMR and than start Timer 1 from T1CON MMR this will load the new value direct or during the Timer 1 is running.
Thanks for the info, that's exactly what I need to know.
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