Quote Originally Posted by richard View Post
pic16 's have one level of interrupt , therefore an interrupt can never be interrupted ...
No, but any interrupt triggered while an ISR is running will be handled once the ISR finishes.

(p.129 16F18877)

Note

1: Individual interrupt flag bits are set, regardless of the state of any other enable bits.

2: All interrupts will be ignored while the GIE bit is cleared. Any interrupt occurring while the GIE bit is clear will be serviced when the GIE bit is set again.
So you can have multiple Timers running at the same time (including USART interrupts and others).

No...?