USART has independent Receive Shift Register, when reception is complete it will then notify the processor by setting RCIF, if interrupt is enabled, it is the interrupt service routine that takes processor time not the serial data reception.
USART has independent Receive Shift Register, when reception is complete it will then notify the processor by setting RCIF, if interrupt is enabled, it is the interrupt service routine that takes processor time not the serial data reception.
My intention is to know the time available for the ISR to read data and then for the other routines to process it before the next one arrives in a hardware serial port peripheral.
of course 9600 baud is approx. 1 ms but it does not mean it will take 1 ms of your processor time (even a sw uart will not) or you only have 1 ms to process data, it depends on your programming style