IRMCK099 chip, through the JTAG interface to access and control ,everything is OK. But can not be accessed through UART (pin30/31). The signal sent to pin30 is normal, but pin31 has no output (ALWAYS 1). The access information of the JTAG interface shows that the UART LINK Break!
* Is there any reason why 099 does not respond to UART information?

Can you help solve the problem as soon as possible? thank you!