Just A couple of Questions

1-when using serial port to send out 1 start bit, 9 data bits and 1 stop bit, where does the ninth bit come from?

2- Can a program use RETI instruction without using interupts? Explain your answer.

Thanks

1. You cant select 9bit data at any device (PC, microcontroller etc)
2. Yes you can, but you cant use RET for interrupts. Because the RETI do the same function as RET and it also clear the Interrupt flag.