Question: Will it cause a problem if I have an ISR that calls another function and I don't specify which register bank the INT0# ISR uses with the "using" statement? What is the importance of specifying the register bank for the ISR?
Answer: Register banks and ISRs are key to handling context switching rapidly in the 8051 family. Context switching is the activity involved in moving from one task to another when an interrupt occurs. Typically, if you don't use the 'using' directive it shouldn't be a problem.
Note: Calling a function from within an ISR could potentially have some shortcomings.
