(1)Make sure that you are checking the correct output terminal.
To check if the terminal is correct or not, set the TXD terminal to the general-purpose port output, change the output from “H"→ "L" →"H", and see if the signal changes accordingly.
(2) Make sure that SCI module stop bit is released.
For products with the write protection function, release the write protection before writing the module stop bit.
(3) For products with MPC, it is necessary to set the PMR register of the IO port. Check the above register.
(4)Check if data is written in the TDR register.
When the TDR register is written during TXI interrupts, interrupts may not be generated properly.
Check the ICU IEN register, IPR register, IR register, CPU “I” flag, and SCI SCR register.
(5) The Development Environment (IDE) simulator may be in use.
Make sure that the simulator is not used for debugging.