I'm working on project that need use of 6 interrupts. I am using arduino mega2560. My plan is to use INT4 and INT5 on digital pins 2 and 3. I want to split other 4 interrupts into two groups of two, because they have similar response, so they can be easily handled by one function. I am thinking about using pins 10,11(PCINT4, PCINT5) and A15, A14(PCINT23, PCINT22). My worries: Can pin change interrupt on pins 10, 11 somehow affect SPI on pins 50-53, because they are on same port? Do SPI use pin change interrupts? Is the reception handled purely by hardware? Same question is for USART. If a were to use digital pins 14, 15 (TX3, RX3) as interrupt pins(not USART), would it somehow interfere with USART on digital pin 0(RX0) because they are handled by same PCINTx_vect?
Can pin change interrupt on pins 10, 11 somehow affect SPI on pins 50-53, because they are on same port?
They are on different pins, you should be okay
pin10 - PB4
pin11 - PB5
pin50 - PB3
pin51 - PB2
pin52 - PB1
pin53 - PB0
It doesn't matter if they are on the same PORTB as long as you have them on different pins