My program is executing a hardware interrupt reading the serial keypad and I want to turn on the display every time the keypad is pressed. This requires sending a command to the display on the same serial channel. Trying to generate a transmit interrupt after reading the keypad but 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.