INT 0cH is a hardware-generated interrupt (IRQ 4) forced by COM1 or COM3
when it is done sending or receiving a byte of data.

  CPU Exception Interrupt  
286+ computer execute INT 0cH when the CPU is in protected mode and it
detects a stack access that is outside of the bounds of the SS selector.

Protected-mode operating systems can watch for this and increase the size
of the stack.

- -

INT 0cH: IRQ 4 COM1/3 / Stack Overflow