MC9S12DP512 Software Interrupt

My program is executing a hardware interrupt reading the serial keypad and I want to turn on the display which uses the same serial port and interrupt service routine.  Trying to generate a transmit interrupt before the receive rti instruction executes causes the system to hang up. Is there any way to implement a software interrupt so that after the serial receive hardware interrupt finishes the software interrupt will then use the serial transmitter to turn on the display? My programming is in assembly code.