Specifications

2 RS232 I/O Support
2-6
Note COM1 and COM3 share interrupt line 4. Similarly, COM2 and COM4
share interrupt line 3. To provide maximum performance, the COM port
interrupt line on your target PC used for serial communication is disabled
while real-time tasks that include RS-232 blocks are executing. This also
means that when COM1 is disabled, COM3 is also disabled since they both
share the same interrupt line. For this case, you would have to use either
COM2 or COM4 as your RS-232 I/O device.